i
THE UNIVERSITY OF NEW SOUTH WALES
AUTOMAT 1 ON IN BROADCASTING STUDIOS
BY
A. S. GRAY
.Submitted for the degree of Master of Engineering
on 3rd March, 1972. UNIVERSITY OF N.S.W. ]
311S7 16. MAY 72 I LIBRARY ii
CERTIFICATE
This is to certify that this thesis has not been submitted for a degree or similar award to any other University or Institution.
A. S. GRAY iii
ACKN QWLEDGSM3NT
I wish to thank the Australian Broadcasting Commission and especially Mr. K. N. Middleton, Controller of Technical
Services for allowing this work to be undertaken, I would also like to thank my Supervisors, Dr. John Hiller of
University of New South Wales and Mr. Carl Wilhelm of A.B.C. for their encouragement and patience. I must state however, that the responsibility for statements made herein rests solely with myself. iiKe finally, I would^to thank ray wife for her help in typing the thesis.
NOTE
A peculiar difficulty in writing the thesis was the usage of the term "program", which is used both in broadcasting and in computing. I have used " programme " to mean the set of broadcasting items to be presented and " program " to mean the set of instructions executed by the computer. SUMMARY
Broadcasting is a form of communications in which emphasis is placed on the uninterrupted transmission and smooth presentation of material, rather than the speed of message handling. Broadcasting entities range from one studio- transmitter stations to decentralised studio network which exchange and merge items to suit a particular programme of operations. The sporadic heavy demands on broadcast operators controlling presentation lead to errors in production and make uneconomic use of staff. Automation offers advantages of reliable operation and fast response to control time-sensitive operations which are mainly mechanical tasks. Errors can be minimised and staff released to make more artistic contributions. Broadcasting automation systems range from permanently-wired event sequencers to large information-processing computer systems such as UHKfs, for resources control. The automation system described here utilises a small process control computer system which costs about $60,000 including auxiliary units such as disc memory and display terminals. Three important features considered are an accurate reliable clock system, a method of entering and storage of operations schedules using alphanumeric displays and systems of automatic time announcements. V
TABLE OF CONTENTS PAGE
PART A
DESCRIPTION OF BROADCASTING- SYSTEMS AND OPERATIONS 1
CHAPTER 1
INTRODUCTION - BROADCASTING AS A FORM OF COMMUNICATIONS 2 1.1 COMPARISON WITH OTHER FORMS OF COMMUNICATIONS SYSTEMS 4 1.2 USES AND USERS OF THE BROADCASTING SYSTEM 9 1.3 CLASSIFICATION OF BROADCASTING ITEMS 13 1.4 THE SENSE OF HEARING 21
CHAPTER 2 THE DEVELOPMENT OF BROADCASTING 39 2.1 RADIO BROADCASTING 40 2.2 WIRE BROADCASTING 42 2.3 STUDIO OPERATIONS AND EQUIPMENT 44 2.4 AUTOMATION SYSTEMS 50
CHAPTER 3 PRESENT TECHNICAL OPERATIONS SYSTEMS 72 3.1 METHODS OF ITEM PRODUCTION 74 3.2 METHODS OF PROGRAMME ITEM PRESENTATION 83
3.3 CONSTRAINTS ON TIMING OF OPERATIONS 90
3.4 TECHNIQUES OF ITEM PRESENTATION 94
3.5 MANUAL SYSTEMS OF OPERATION 97 vi
PART B
AUTOMATION SYSTEMS FOR BROADCASTING 103
CHAPTER 4
THE CASE FOR AUTOMATION 104
4.1 THE TASKS IN A BROADCASTING STATION 105
4.2 TYPES OP AUTOMATION SYSTEMS 106
4.3 RELIABILITY OP AUTOMATED SYSTEMS 111
4.4 DEFICIENCIES OP THE MANUAL SYSTEMS 121
4.5 ADVANTAGES AND DISADVANTAGES OP AUTOMATION 123
CHAPTER 5
DESIGN OP A COMPUTER CONTROLLED SYSTEM 126
5.1 SERVICING OP TASKS 128
5.2 DERIVATION OP OPERATIONAL TIME 132
5.3 SCHEDULING OP OPERATIONS 136
5.4 ITEM PRESENTATION METHODS 152
5.5 THE COMPUTER AND PERIPHERALS 186
5.6 REVIEW OP COMPLETE SYSTEM 192
CHAPTER 6
STUDIO BROADCASTING OPE.RATIONS 194
6.1 PREPARATION OP ITEMS FOR PRESENTATION 195
6.2 ON-AIR COMMENCEMENT 212
6.3 OPERATIONS DURING BROADCASTING 223
CHAPTER 7
CONCLUSIONS 22?
7.1 COSTS 227 7.2 BENEFITS 227 vii
APPENDIX A
IN -■ BAND SIGNALLING 229
APPENDIX B PAPER : "FACTORS IN THE PURCHASE OF A SMALL PROCESS 243 CONTROL COMPUTER”
(Submitted as supporting material) PART - A
DESCRIPTION OP BROADCASTING SYSTEMS AND OPERATIONS 2
CHAPTER 1
INTRODUCTION - BROADCASTING- A3 A FORM OP COMMUNICATIONS
1.1 COMPARISON WITH OTHER FORMS OP COMMUNICATIONS SYSTEMS 4 1.2 USES AND USERS OF THE BROADCASTING SYSTEM 9 1 .2.1 Profit -■ Seeking Broadcasters 10
1 .2.2 Non-Profit-Seeking Stations 11
1.3 CLASSIFICATION OF BROADCASTING ITEMS 13
1.3.1 Material. Used as Broadcasting Items 13
1.3.1.1 Entertainment Material 13 1.3.1.2 Information - disseminating Items 16
1.3.1.3 Composite Items 19 1.3.2 Methods of Item Production 19 1.3.2.1 "Packaged" Items 20 1.3.2.2 Occasional - demand Items 20
1.3.2.3 Heavy - demand Items 21 1.4 THE SENSE OF HEARING 21
1.4.1 The Physics of Sound 21 C\J • • Hearing : The Perception of Sounds 25
1.4.2.1 The Attributes of Hearing 25 1.4.2.2 Some Phenomena of Hearing 28
1.4.3 Constraints of Hearing on Broadcasting 33
CHAPTER 1 - REFERENCES 36 - 3 -
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CJOMMMICATtotfS
A MESSAGE
FIC. /-/ COMMUNICATIONS SYSTEM - 4 -
CHAPTER 1
INTRODUCTION - BROADCASTING AS A FORM OP COMMUNICATIONS 1.1 COMPARISON WITH OTHER FORMS OP COMMUNICATIONS SYSTEMS Communication is the act of passing a message, or item of information, from its source to a destination. A communications system achieves this by coupling the source and destination by means of a transmitter, a receiver and a channel between them. 1 * This is illustrated in figure 1-1, on the opposite page. The term ’’system" implies an assemblage of diverse elements or units that are mutually 2 related and interdependent.
A typical task of a communications system is that of message switching. The system is required to route messages from a number of sources to specified destinations. The messages are variable in the amount of information contained (measured in binary units, called "bits") and in the rate at which they arrive for transmission. The linking communications channel has a fixed capacity to pass messages, measured in bits per unit time. The aim is to despatch the messages in an error-free condition as quickly as possible, so the success of a message-switching system-design is measured in terms of the delay a message experiences between the time it is presented by the source to the time it reaches its destination. Broadcasting is another method of communication, which has a different set of aims. In this method a single transmitter serves a small number of sources, and communicates * References are located at the end of each chapter - 5 - with a large number of destinations simultaneously; hence the name "broad-casting". This is a convenient means by which an individual or small group can disseminate information to a large population of destinations, and so it is exploited both by government agencies and by commercial and other common-goal groups.
Whilst broadcasting is an instrumental form of communication^ (that is, the source desires a response from the destination) assessment of the response is not immediate, so that at the instant of broadcasting the act is a one-way, one-to-many operation. However, in cases where the set of possible destinations, the "audience" has a choice of a number of transmitters with which to link, then the wishes of the audience influence the material broadcast by the competing sources/transmitters (stations). In general, audiences tend to assess material in terms of its entertainment value^. Thus a criterion for successful operation becomes:
"the most pleasing, or entertaining presentation of material being broadcast". Sections of items which are boring or unintelligble must be avoided. For example periods of silence between items and loss of parts of a message because another message interrupts the first are distasteful to audiences, so broadcasters try to avoid these blemishes.
So the station operator, or broadcaster, becomes primarily concerned v/ith the "smooth" flow of items to the communicant ion channel, rather than with the rate of flow of messages; the - 6 - rate of message passing in broadcasting can be slow or rapid, provided the result is not disjointed. To achieve smooth presentation the broadcaster must know the duration of each item of information and the intervals of time, or time slots, available for item presentation so that he can plan a schedule of operations accordingly. In addition, a competing broadcaster must communicate to his potential audience details of items to be broadcast. This enables the audience to plan its schedules of listening, but imposes the necessity on the broadcaster for synchronisation of his operations with his advertised programme, or schedule of items. If mis-timing does occur, he is obliged to ensure that items do not commence early, by the use of short unadvertised items as "fill-ins”. Hence the broadcaster has two operational goals: (1) adherence to his advertised schedule of items to be broadcast. (2) pleasing continuity, or flow, of programme items. In order to compare more closely the two forms of communications systems, message switching and broadcasting, consider the following example. Let the message length in the message switching system be exponentially distributed about an average of 1/n bits. Also, let the arrival rate of messages be exponentially distributed with an average of
1 per second.' (The exponential distribution is chosen because it is time independent, i.e., has no memory of previous - 7 - events). The communications channel has a certain capacity to pass messages, measured in hits per unit time. Taking the capacity as C hits/second, messages will he despatched immediately on arrival, provided the instantaneous arrival rate of messages never exceeds the channel capacity. If the arrival rate does transiently exceed the channel capacity hut the average arrival rate (of 1/n hits/second) is less than the channel capacity (ie l/n
In a broadcasting system a time slot of T seconds is desired to he filled, this being the equivalent of the channel capacity. Unfortunately the true duration of the item is unknown, although the presumed duration is given. Let the presumed duration, d, he measured in time units called 8 - protime (for example, proseconds) and let the relationship between protime and true-time have an average of p proseconds/ second. The true-time duration, equivalent to average arrival rate, is then d/p seconds. The utilisation factor,
is 3 p T ...(1.2) and is the fraction of the slot which is used to transmit the item. Since congestion occurs if S >1, the average true-time duration of the items must be less than the slot duration.
As an idle channel is not permitted in a broadcasting system, optional-use items are required to fill-in any gaps. The use of these is similar to the service of a queue of low priority messages when the arrival rate of messages is less than the channel capacity. In the broadcasting case the
"queue" is really unwanted material whereas in message switching all messages must eventually be sent. The main difference between the two systems, in this analogy, is that as a condition of congestion is approached, the queue vanishes in the broadcasting system and increases continually in the message switching system.
In comparing the two systems, it is evident that time, in the form of item duration, is equivalent to information rate. Prom estimates of p the design of time slots can be performed. - 9 -
For example, if p was known to have a value:
p = 1.02, so that the item is transmitted at a faster rate than normal, and the presumed duration, d :
d = 600 proseconds.
Then true duration = d/p = 588 seconds and a slot of 588 seconds could be used. If the slot were originally made equal to the presumed duration (T = 600 seconds) then 12 seconds of fill-in would be necessary.
However, it is usual to know only modulus of the error, viz. 1 - p The slot is then found by taking the worst case, greatest duration expected. This is calculated by
T = d (1 + 1 - p ) seconds ...(1.5) = 600 (1 +1 -1.02) =612 seconds. In this case, fill-in material of 24 seconds (ie 612-588) would be needed.
1 .2 USES -AHD USERS OF THE BROADCASTING- SYSTEM
In the United States of America a broadcasting station which applies for an operating licence has to state that it will serve the public interest, convenience and necessity.
To perform these duties the station produces items of two tyi^es:
(a) entertainment, (b) information dissemination. 10 -
Whether one type or other is emphasised generally depends on the motives of the controlling interests of the station.
Stations can he controlled either by profit-seeking concerns or by government bodies. Most countries select one or other method in pure form, although a few countries such as Australia, 7 Canada and Japan authorise a mixed system.
1.2,1. Profit-Seeking Broadcasters
Commercial ventures seek to make profits by "selling” short periods of broadcasting time to other companies or bodies that wish to publicise (by advertisement) some item.
The bargaining rate for the sale depends on the number of receivers likely to be linked at the time of the advertisement to the station*s transmitter. To increase the rate, the commercial station attempts to attract the largest audience by broadcasting material which is popular. Items of transient appeal such as ’’fashionable" music, and items of comedy use a large proportion of available time since size of audience is increased. The competition between stations broadcasting to the same area tends to increase standards of presentation of items, in terms of the criterion of more pleasing presentation.
Some countries such as in Central and South America have relatively few, though large, broadcasting corporations.
Others such as the United States of America have legislated to ensure that the number of stations under single control is limited^. 11
This causes a multitude of small, low budget operations, stations. This would be expected to lower the sense of competition between stations since it more closely 9 approximates perfect competition than the system of a few large operators. However, the spatial limitations of effective reception reduces the number of competitors and sharpens the sense of competition, although station control is diversified, the advantages of centralised production have caused the growth of "national networks'* in the United States, There are three national networks, ABC, CBS, and NBC which sell their items, together with advertisements, to the independent regional stations. A degree of co-operation in planning now occurs to allow the syndication of items to the local stations. The sense of competition between the network is high so, as a matter of prestige, offerings are made which cost more than is recouped in advertising charges. These items are in the fields of information and special events. To summarise, commercial broadcasting is effectively a mass medium, dependent for economic success on the attracting of large audiences.^ 1,2.2 Non-Profit-Seeking stations
Stations administered by government departments, non- profit- seeking private organisations or statutary authorities are less likely to be influenced by changes in "fashionable tastes" than are commercial ventures. Thus more emphasis is able to be 12
placed on the dissemination of information and less accent need be given to entertainment. The operations of non profit making stations are financed from public or private subscription, grants from government funds or from receiver licence taxes. The stations can be used to:
(a) promote the policies of the station*s controlling group;
(b) complement the popular bias of commercial stations by
providing non-profitable items such as those which attract
a small number of listeners only, or educational items;
(c) act as a supplier of information independent of government
and private enterprise.
Type (a) includes the use by private groups who wish to present information about the religious or philosophical thought of the group or by governments who use the station to implement party ideology (for example, to promote regional unity or provide a measure of competition with commercial broadcasting stations). Type (b) is sponsored by governments as a public utility, the station often acting in concert with government departments. Type (c) is usually a part of a democratic system of government although the immediate reasons for establishment could include political expediency.
When stations are expected to fulfill more than one of the above uses difficulties of interpretation of the role of the 11 station can arise. This is discussed by koorhouse , who considers the operations of the Australian Broadcasting
Commission in implementing the roles listed as (b) and (c) above. - 13 -
1.3 CLASSIFICATION OF BROADCASTING ITEMS
Items of a broadcasting programme can be classified according to two criteria:
(a) the nature of the material composing the item, and the
type of audience served;
(b) the impact of the production of the item on the resources
of the broadcasting station's presentation sjrstem*
Both methods can be used to indicate the type and degree of interaction required of the broadcasting operations control system for successful communications. Method (a) exposes the characteristics of the material within the item and its effect on operations, whereas method (b) considers the effects of production methods.
1.3.1 Material used as Broadcasting Items
Programme items cover a wide spectrum of human interests including popular entertainment, educational and generally informative components. The material can be classified as:
(a) primarily entertainment;
(b) primarily information dissemination;
(c) a composite, or mixture of (a) and (b).
1.3.1.1 Entertainment Material
Material classed in type (a) as entertainment includes:
(i) music;
(ii) drama; 14 -
(iii) sporting and other "open-air" events; (iv) participation items such as a quiz or competition. Music utilises the complete range of the technical characteristics of a broadcasting channel. G-reat care must be taken that amplitude-frequency linearity, amplitude-gain linearity and the dynamic range of loudness variations are optimised according to present technical limitations to obtain best fidelity. Music is also particularly sensitive to variations in the rate of progress of protime with respect to true time. Such variations do not normally occur in live presentations, but occur during the reproduction of stored material. The variations cause a change in the frequency of a musical note. If the frequency change is constant, the effect is noticeable only to listeners with "perfect pitch"
(discussed in section 1.4). However, if the frequency of the note itself varies, the effect can be very noticeable, being called "wow" or "flutter", depending on whether the variation is slow or rapid. The reduction of such variations can appreciably increase the cost of equipment used to broadcast the musical item.
A musical item develops a theme and so contains position- defined information, but the information is not compact because of repetitions and use of standard structure. This reduces the impact of loss of a portion of the broadcast due to hardware or operational failure, although the sense of continuity is necessarily impaired. - 15 -
Drama consists of spoken words, occasionally augmented by aural effects such as music or sounds appropriate to the action being portrayed. The demands on technical quality are not as stringent as those for a musical item, but the information rate is much more compact being approximately that of speech (e.g., for English, about one bit per word).
Because of this a failure in the broadcast for even a short period can be catastrophic since the listeners' comprehension of the item is very much affected. A dilemma then arises when the broadcast is re-established as to whether to continue directly on with the item, as though nothing had been missed, in order to preserve synchronism with the prepared schedule of broadcasting events. The alternative is to re-commence at the point where failure occurred so that no material is lost, but this would cause a loss of synchronism unless other items were deleted.
Outside, or "open-air", events are usually spoken descriptions of particular activities such as sporting competitions, in which physical prowess of individuals and co-operation of teams is judged. The rate of presentation of information varies considerably throughout the item, because the activities are usually synchronised to some time table independent of the broadcasting operations. Thus interruptions to the broadcast at times of high rate of presentation of information can be very annoying to listeners, but the information can be repeated, or summarised later, during 16 -
a slow rate period. Since external events are less reliable than, the internally controlled items, it is usual to arrange an alternative programme of items to be ready as a substitute.
Items with non-professional participants, such as quiz and panel-game shows, do not pose any special engineering problems. However, live presentations which include audience or listener participation have a problem of controlling the material presented by these participants. Some method of allowing the censorship of material judged to be objectionable is necessary. This is often achieved by introducing a delay of some period, either by temporary or permanent storage, so that consideration and action can occur if necessary. Also, it could be mandatory to keep a record of such items against the possibility of legal proceedings.
1.3.1.2 Information - disseminating Items
Items intended to be informative can be grouped generally as:
(i) topical;
(ii) governmental;
(iii) commercial;
(iv) educational;
(v) broadcasting station information.
Topical items include time announcements and signals, and news copy and discussion of news. Both time and news announcements can be scheduled or unscheduled (random 17 -
occurrence) items. Scheduled topical items, which could
include weather reports, are usually started at a significant
time such as the "hour”, "half-hour" or "quarter-hour" and a
time signal, such as the sounding of a musical tone, is often
used to indicate the exact moment of the time value (e.g., for
the "hour" - zero minutes and seconds). Such scheduling imposes
the constraint that the broadcasting operations should he
correctly timed at the instant before the announcement, although
in practice, if an item is running significantly late the time
announcement and signal are often superimposed over the item's
material. Unscheduled time announcements are either included
as material within an item or are inserted during the pauses
between items.
Because of the desire by nev/s reporters to be absolutely
topical, there is a propensity to request unscheduled news
broadcasts, or "nev/s flashes". These can be inserted into the
programme either by deleting scheduled material or by delaying
the schedule. The question of which method to choose depends upon the relative priority of the news flash and the scheduled
item. One solution, which wastes a portion of the time
available for broadcasting, is to allow a certain number of
scheduled items to be optional. The news flashes can then be
inserted in place of these until no deletable items remain.
G-ovemmental items include official announcements and the broadcasting of parliamentary proceedings. The former are
short items such as the notification of specific duties of the 18 -
citizens (e.g., compulsory voting in elections). Parliamentary
sessions can sit for several hours and since it is likely that
regulations covering the broadcasting of proceeding could
stipulate that the complete session must be broadcast,
considerable time is used. Also, the end of a session is rather unpredictable so planning of schedules is difficult.
Commercial items consist mainly of reports on prices and
quantities associated with sales. The reports include stock market and farm and other primary industry produce and can be
of fairly general interest.
An educational item can be defined as one containing
"information which society at large would regard as being generally desirable for the average person to know, especially
such types of information as tend to improve the individual himself and enable him to keep pace with the gradually rising 1 2 level of social knowledge and culture." Educational items are produced for general consumption and also directed towards specific groups such as school children. Material is usually made up of spoken words, and is rather similar to drama broadcasts except that the information rate is slower.
Broadcasts intended for use by schools are scheduled during school hours (i.e,, daytime listening).
In addition to the above types of items, the broadcasting station uses a part of the available time for announcements on its own behalf. These consist of call signs identifying the station, signals meant to prompt the commencement of items, 19 -
publicity concerning future items to be broadcast, and paid advertising. To some extent the use of these items is optional giving station operators the opportunity to adjust operating schedules. Paid advertising is often sold on the basis of a specific broadcasting time, and prompting (or cueing) signals are also needed at a specific time, so these cannot be deleted.
1.3.1.3 Composite Items
Composite items are those which include components of both entertainment and information dissemination.
These items are directed to particular groups in the community such as young people, housewives, and people living in rural areas. Another special group are the religious denominations.
Both devotional and informative items are broadcast, particularly on Sundays and in the late evenings. Material for these special groups do not pose any further difficulties than those discussed previously.
1.3.2 Methods of Item Production
The second method of item classification is based on the amount of work required of the operations staff to present the item. Some items require a minimum of attention only, and are styled "packaged", or "self-contained" items. Others require some attention during broadcasting, but demands are sparse enough to allow duties to be shared with other tasks. A third 20 - group requires constant, or "dedicated" attention.
1.3.2.1 "Packaged" Items
"Packaged" items are those which arrive at the broadcasting operations centre as a single entity. They are produced outside the centre, either as a live item from within the station premises, or are recovered from some storage system.
The recording of the item into the storage could be performed at any place, and man\r such items are purchased from overseas organisations, but these could require pre-processing to be made compatible with local recorded items. The recorded item could be originally produced in a number of separate parts, but these would be joined to form a single entity before being broadcast.
To effect the broadcast, the only executive operations needed are those to signal the commencement of the item and detect the conclusion of the item. In addition, there is a need during the broadcast to monitor the transmission to detect any deterioration in the technical quality.
1.3.2.2 Occasional - demand Items
Items which are not comr>lete, but require a few short linking operations (possibly with announcements), form one type of occasional demand items. For example, an item could consist of several interviews recorded at separate times and places and concatenated during the broadcast. Another type includes items 21
which are liable to suffer breaks in transmission due to
equipment failure or non-occurrence of material. Particular
cases are outside broadcasts such as cricket matches and
parliamentary proceedings. Here the demand for attention
could be unpredictable so a signalling system is required.
There must, of course, be sufficient equipment to enable the
components to be assembled into an item, and the operations in
1.3.2.1 must be performed as well.
1.3.2.3 Heavy - demand Items Items can be pro duced at the time of broadcasting by
concatenating the elemental material used in the item. An
example is that of a musical show in which short duration recitals, say three minutes, are played, and are preceded and followed by announcements regarding the recital and also material such as time announcements, advertisements and call- signs. The act of production demands the dedicated attention of operational staff because of the short lapses of time between elemental events. The operations noted in 1.3.2.1 and 1.3.2.2 also must be carried out.
1.4 THE SENSE OF HEARING
1.4.1 The Physics of Sound
Sounds arise by the variations in the density of a fluid medium, such as air. The sound is propagated from one location to another by wave motion in the medium, in which - 22
longitudinal compressions and rarefractions of the air alternate in time and position. If the variations are periodic in nature they are called tones whilst those which are aperiodic are termed noises. Periodic sounds have four attributes:^ ^ (a) intensity ;
(b) frequency ; (c) phase ; (d) waveform. Intensity is the average power (i.e., rate of energy flow) per unit area, which is often measured in decibels relative to a standard intensity. The standard is usually chosen for convenience to be that which is equivalent to minimum _ £ audibility, which occurs at a maximum excess pressure of 2x10 Newtons/sq,metre (2x10"^ dynes/sq.cm.). Frequency is the number of compressions (or rarefractions) which pass a fixed location in unit time. Conversely, the time lapse between successive similar points of the alternation cycle is called the period, and the position lapse (or distance) between them is the wave length.
Phase is a measurement of the advancement of the variation along the cycle of alternation, compared to some arbitrary point on the cycle. It can also be used as a comparison between two waves by assessing the relative advancement of one with respect to the other.
Waveform relates to the shape of a graph of the variation - 23 -
as a function of time or position. The simplest waveform
has a sinusoidal function shape. Other more complex periodic waveforms can he expressed by using Fourier analysis as a sum of component sinusoids with the characteristics (a), (b) and (c) listed above. The frequencies of the components show simple integer ratio relationships with a minimum or fundamental
frequency, although not all "over-tones” (harmonics with ratio
1 : 2, 1 : 3 and so on) are necessarily present. The wave motion characteristics of sound give rise to the properties of scattering, such as reflection, refraction and diffraction. The use of Huygen's Principle^ leads to Snell's laws of reflection and refraction. Acoustic reflections (echos) are an important factor in the design of studios and auditoria. Diffraction of waves around an obstacle occurs because of scattering, the effect being dependent on the relative size of the wavelength and the object. For short wavelengths the forward scattered waves cancel (destructive interference) so that a shadow forms. With long wavelengths scattering is isotropic and no shadow develops, and when they are comparable, diffraction patterns of minima and maxima occur. The case of scattering around the human head is interesting since below about 512 Hz there is little shadowing effect but beyond this the effect is increasingly evident. Another effect of the scattering of a number of waves of different frequencies is that the higher frequency waves increase in relative intensity (analogous to the explanation of the blue colour of - 24 -
LDUDVZSS (PHorJS)
Vj ^ tzo ^ \
Jsi V no
GO 100 600 /COO 2000 6000 /Ctfioo 20,000
threshold 00
MDi&u/rY ^
ell L2 comm oejjml LM/mi (AFT£/l kERAhJSK 27 ) - 25 -
sky). This causes an apparent increase in the pitch (or
perceived frequency) heard by an observer. ^
1.4.2 HEARING- : THE PERCEPTION OP SOUNDS
1.4.2.1 The Attributes of Hearing
The sense of hearing is the brain1s interpretation of
electrical nerve impulses transmitted from the ear, which acts
as a detector of air pressure variations. The ear itself has
characteristics which limit the range of sounds which can be
detected. The resultant of detection and interpretation is
called perception, and this final "image" can differ
considerably from the objective sound. The study of these
effects is called psychoacoustics.
Auditory response shows three attributes:
(a) loudness ;
(b) pitch ;
(c) timbre.
The loudness of a sound is dependent mainly on its
intensity, but is also affected by the frequency and composition of the wave. The unit of loudness measurement is the "phon", which is established by reference with a pure 1000 Hz tone of apparent equal loudness. The number of phons is then equal to the intensity ratio (in dB) referred to the standard —5 16 intensity given by 2x10”*^ Newtons/sq.metre excess pressure. 17 A graph of equal loudness contours is shown in figure 1-2, which is plotted on axes of intensity level and frequency. - 26 -
Z400
zooo-
tzoo
10O ZOO 400 1000 ZocO 40cO (0,000?
FfZ£QU£hfC y (£z:J
m. i-5 relation mm pm and frequence - 27 -
The minimum and maximum limits of loudness perception are called the thresholds of hearing and of pain respectively. Between these the perceived loudness of a sound varies roughly as the logarithm of its energy. Pitch is the attribute which admits of a rank ordering
on a scale ranging from low to high, which correlates strongly with objective measures of frequency. 1 8 Pitch is not quite equivalent to frequency, as the graph in figure 1-3
shows. 1 9 This indicates the non-linear relation between frequency and pitch of a pure tone 40 dB above threshold, where the pitch is measured in "mels", arbitrarily adjusted to be equal to the frequency at 1000 Hz. An important property which affects broadcasting is that the differential of pitch (the minimum change which is audible) is very small, in fact a 2 Hz increase in frequency causes an increase in pitch. 20 Timbre is the quality which distinguishes the sound of one type of musical instrument from another. The differences arise because each tjrpe generates a unique set of harmonics with particular relative energies when a note is sounded.
Since harmonics distinguish instruments, each sound can be synthesised by combining harmonics in the correct numbers and relative energies, and this can be performed on an organ by selecting different pipes. The timbre depends only on the relative energies of the various harmonics and not on their phase-differences, which have no effect on the ear. This insensitivity to phase difference is known as Ohm’s law of - 28 -
hearing.^
1.4.2.2 Some Phenomena of Hearing
Some effects important in the perception of hearing arise due to combination of sounds which occur together. These can be classified as:
(a) beats;
(b) combination tones;
(c) masking.
Another two phenomena of interest to broadcasters are:
(d) perfect pitch;
(e) localisation of sound.
Beats and combination tones are produced by the intermodulation, caused by the non-linear characteristics of the ear, of tones of different frequencies. If the difference in frequency between two tones is less than about 50 Hz then variations in loudness are perceived at this difference frequency. The loudness variation is called a ’’beat" and the effect is usually considered to be unpleasant. This phenomenon is used to tune two notes to the same frequency by eliminating any beat frequency tone. Beats as low as 1/30 Hz can be perceived under good listening conditions.
If the primary, or incident, tones are separated in frequency by more than about 50 Hz then additional tones are heard. These are called combination tones and are the summation and difference terms resulting from the non-linear - 29 -
££V£L OF TONE A
/6C0 ZOOO 24-00 -520 0 4000
FREQUENCY Of T O A/E 3 [Hz.)
LFQFNP :
TONE A - MASK/NO TOME TONE 8 = /N/TfAL TONE'
REOioN l ~ TONES A & B EEE/oN 2. - TONE A OA/o y
REE/ON 3—A}3& O/EEEEENar toa/ES ReE/Oa! 4- — A 4? D//ZTERENCE TO A/E S
Regsoa/ sr - Ff/XTC/RE &/= TO/VE'S
F/C. f-4- MAS Km OF PUKE TOUTS (AFTfR B££A/v£/c zg) - 30 -
interaction. The difference tone is usually more noticeable than the summation because the latter is likely to be obscured by other tones, such as the two primary tones (an effect known as masking). Whether the combination tones are pleasant or unpleasant to hear depends on the degree of harmony between the resultant components, and this is dependent on the approach of frequency ratios to small integer numerator or denominator values (e.g., 3 : 2 or 4 : 3). In practice the more noticeable difference tone aggregates are reasonably harmonious. These effects are sometimes called "subjective tones" although the phenomenon is truely objective in that the extra tones are physically, not psychologically, generated.
Masking is the effect in which the perception of one sound is obscured by another. It is defined as the increase (measured in dB) in the threshold of audibility of one tone in the presence of another. Masking has the properties that: (a) a tone will tend to be masked by a sound of lower pitch; (b) generally, the smaller the difference in pitch the better the masking with the exception that beats will occur as the difference vanishes;
(c) narrow band noise centred on the same pitch will raise the threshold level.
The properties (a) and (b) are indicated in figure 1-4, which shows the masking effect of a 1200 Hz tone on tones of other 22 frequencies.”” There is little masking below about 800 Hz, but a sharp increase occurs as 1200 Hz is approached. Above this - 31 frequency the effect continues, as suggested by property (a).
The notches in the contours at 1200 Hz and harmonics of this frequency are caused by the beats suggested in (b). The ear’s non-linearity produces the effects at the harmonic points.
The notch effect can be avoided by using a narrow band of noise for masking, instead of a tone. The degree to which a band of noise masks a tone whose frequency is near the centre of the band is related to two principal variables, the intensity of the noise and the width of the band. Perfect pitch (also called absolute pitch) is the name given to the ability of some individuals to identify any specimen musical note on the pitch scale. These people can locate a note on the musical scale with a margin of error less than half a semi-tone (a semi-tone is one of the set of notes obtained by dividing an octave into twelve intervals) and so can distinguish the case when an orchestra has tuned to a non standard pitch (e.g., it is "flat"). Studies by Bachem have shown that three types of so-called perfect pitch exist:
(a) absolute; (b) pseudo - absolute; (c) quasi - absolute. p Perfect pitch ability relies either on tone chroma or tone height estimation. Tone chroma is the quality common to all tones in octave relationship and tone height is the position on the pitch scale octave 1, 2, 3 and so on. Those with true perfect pitch (type (a)) use chroma estimation, giving the - 32 -
estimate immediateljr, even when the sound is rich in overtones.
Few individuals onljr make no errors, and errors are usually those of exact octave intervals. Errors of one half-tone are common, probably due to the fact that orchestras tune slightly differently. Pseudo perfect pitch is based on the estimation on tone height and can be acquired by training.
It is not as precise as type (a) and an analysis of errors shows a normal distribution about the correct pitch. 'Quasi perfect pitch is based on an interval estimation using an aural standard. The response to tests is hesitant, and the subject makes use of singing or humming, so singing training is important.
Localisation of sound includes both angular and depth localisation. Whilst some localisation is possible with one ear (monaural), better results are obtained when listening with two ears (binaural).
The sense of direction of a sound, or angular localisation is poor when the sound is nearly opposite to either ear. It improves markedly when the sound source is in a horizontal plane directly in front or behind the person. Possible direction indicating cues of a binaural nature are relative loudness and relative timing (or pha.se) at the two ears. It is generally accepted that at low and medium frequencies
(below about 3 K Hz) loudness variations due to shadowing by the head do not occur, so time cues are important. At high frequencies localisation is cued both by loudness differences - 33 -
and time, or phase, differences associated with the envelope of an37- modulation of tones. Estimation of distance, or depth localisation depends both on loudness and ratio of reflected to direct sound. Sounds lacking in low frequencies appear to be more distant than 26 sounds containing them.
1.4.3 Constraints of Hearing on Broadcasting The potential of broadcasting is constrained by the technical limitations of the communications system, which do not rival the limits of hearing. The spectrum of amplitude levels (called the dynamic range) which can. be accommodated is equivalent to about 60 dB, the high and low level limitations being interference (i.e., leakage, or cross-talk) and background noise respectively. However, human hearing can perceive a loudness range of about 120 dB, and the dynamic range of a symphony orchestra is about 75 to 80 dB. In order to broadcast an orchestral performance the range must be compressed by shaping the amplitude transfer characteristic, either electronically or by manually adjusting gain during soft and loud passages. The audible frequency spectrum extends from about 20 Hz to 18 K Hz in young people, with the upper limit decreasing with age to below 10 K Hz. Nowadays this range can be transmitted but considerations of cost and the need to share limited communications channel space prescribe some - 34 - restriction. A typical range could be 50 Hz to 10 K Hz or up to 15 K Hz. The re-creation of stored item material at a protime rate different to the original gives rise to a shift in the pitch of periodic sounds. As was mentioned in section 1.3.1.1 this can cause two audible effects, depending on whether the difference is constant or varying. A. constant difference causes a constant modification in pitch which is detected only by persons having perfect pitch. Whilst the number of these is small, the proportion of listeners to a musical item with this ability is likely to be high, so the effect is not just a minor irritation. If the difference is varying the effect is noticeable to most listeners as a change in a note's pitch, (i.e., wow or flutter) since the ear is sensitive to a frequency change of 2 Hz. It is sometimes desirable to use the same communications channel for item transmission and signalling. One reason for this is to ensure that the item and its related cueing signals do not become separated and confused with others at intermediate links in the transmission system. In some cases it could be the only practical method; for example, when the signal is intended for use at the final destinations. To avoid interference with the item, the cueing signal could be given exclusive use of part of the channel. The item material, however, tends to occupy the whole channel so the introduction of out-of-band signals restricts the technical quality of the - 35 -
transmission.
An alternative is to use the complete channel for item transmission, hut to introduce in-hand signals which are disguised so they are at or helow the thresholds of perception. Properties of hearing such as variation of threshold of audibility with frequency, time required for tone registration and masking of sounds are possible methods of disguise. Such properties would also tend to lower the maximum signalling rate and increase the complexity of signal receiving equipment. - 36 -
CHAPTER 1 - REFERENCES
1 CLAUDE E. SHANNON and WARREN WEAVER, The Mathematical Theory of Communication, (Urbana : The University of Illinios, 1949), p 5.
2 JOSEPH ORLICKY, The Successful Computer System, (New York : McGraw-Hill, 1969), p 14.
3 VOL MOLESWORTH, Factors in Effective Communication, (Sydney : West Publishing Corp,, 1964), p 15.
4 ROBERT E. SUMMERS and HARRISON B. SUMMERS, Broadcasting and the Public, (Belmont, California : Wadsworth Publishing Co., 1966), p 300.
5 LEONARD KLEIHROCK, Communication Nets, (New York : McGraw-Hill, 1964), p 136.
6 WALDO ABBOT, Handbook of Broadcasting, (2nd edition; New York : McGraw-Hill, 1941), p 91.
7 CANADA, Royal Commission on Broadcasting, (Ottawa : March 15, 1957), p 12.
8 SUMMERS and SUMMERS, op. cit., p 22.
9 PAUL A. SAMUEL3ON, Economics : An Introductory Analysis, (6th edition; New York : McGraw-Hill, 1964), p 474.
10 SUMMERS and SUMMERS, op. cit., p 270.
11 FRANK MOORHOUSE, "The ABC’s Search for Identity," Current Affairs Bulletin, Vol. 46, No. 10 (Department of Adult Education in the University of Sydney, October 1970), pp 147 - 159.
12 ABBOT, op. cit., p 203. - 37 -
13 ERNEST GLEN WEVBR, "Hearing," Encyclopaedia Britannica. (edition of 1962), XI, p 297.
14 FRANCIS A. JENKINS and HARVEY B. WHITE, Fundamentals of Optics. (3rd edition; New York : McGraw-Hill, 1957), p 232.
15 ROBERT BRUCE LINDSAY, "Sound," Encyclopaedia Britannica, (edition of 1962), XXI, p 17.
16 A. J. KING, Technical Aspects of Sound, ed. E. G. RICHARDSON (2 vols; Amsterdam : Elsevier Publishing Co., 1953), I, p 160.
17 R. K. POTTER et al.. Technical Aspects of Sound, ed. E. G. RICHARDSON (2 vols; Amsterdam : Elsevier Publishing Co., 1953), I, p 259.
18 JAMES L. FLANAGAN, Speech Analysis Synthesis and Perception. (Berlin : Springer-Verlag, 1965), p 107.
19 R. K. POTTER et al.. op. cit.. I, p 263.
20 HARVEY FLETCHER, "Loudness, Pitch and the Timbre of Musical Tones -and Their Relation to the Intensity, the Frequency and the Overtone Structure," The Journal of the Acoustical Society of America. Vol. VI, No. 2 (1934), p 66.
21 JAMES JEANS, Science & Music, (London : Cambridge University, 1937), p 86.
22 R. K. POTTER et al., op. cit., I, p 266.
23 JAJ ES p. EGAN and HAROLD /. HAKE, "On the Masking Pattern of a Simple Auditory Stimulus," J. Acoust. Soc. Amer., Vol. XXII, No. 5 (1950), p 629.
24 A. BACHEM, "Various Types of Absolute Pitch," J. Acoust. Soc. Amer., Vol. IX, No. 2 (1937), pp 146 - 151. - 38 -
25 A* BAOHEM, "The Genesis of Absolute Pitch," loc. cit., Vol.XI, Mo. 4 (1940), p 436. 26 R. K. POTTER, et al., op. cit., I, p 268. 27 LEO L. BERAMEK, Acoustic Lieasureraents, (Mew York : John Wiley, 1949), p 200.
28 Ibid.. p 203. - 39 -
CHAPTER 2
THE DEVELOPLiENI OP BROADCASTING
2.1 RADIO BROADCASTING 40 2.2 WIRE BROADCASTING 42
2.3 STUDIO OPERATIONS AND EQUIPMENT 44
2.3.1 Studio Development 44 2.3.2 Technical Equipment 46 t^\ CM • • Current Trends 49
2.4 AUTOMATION SYSTEMS 50 2.4.1 Hard-Wired Sequencers 52
2.4.2 Stored Program Continuity Control 55 2.4.3 Large Systems 60
CHAPTER 2 - REFERENCES - 40 -
CHAPTER 2
THE DEVELOPMENT OF BROADCASTING
2.1 RADIO BROADCASTING
Radio communication was developed by G-uglielmo Marconi and others during the 1890*s from the mathematical and experimental works of the previous twenty years by J. Clerk i Maxwell and by Heinrich Hertz. The earliest telephony broadcast was made by R. A. Fessenden on 24th December 1906 in the United States of America, the transmitter being an 2 Alexanderson alternator of 1 KW power at a frequency of 50 KHz.
The results were of poor quality, but advances were made with the invention of electron devices such as J. A. Fleming*s diode and Lee De Forest*s audion (or triode).
Much of the early experimental work was carried out by amateurs, until transmissions were banned during World War 1.
After the war, amateur work continued, but commercial organisations also showed interest in broadcasting using radio.
At this time the differences between the broadcasting systems of the U.3.A. and G-reat Britain began to form. In the U.S.A. hundreds of stations commenced operations within a narrow band of radio frequencies, with chaotic results. Attempts by the government to control this led to a successful court challenge by a Chicago radio station, which precipitated the formation of a Federal licensing commission in 1927. Acts of Congress established broadcasting rights and defined specific channels within the frequency spectrum to be used by single stations - 41
within a geographical region*
The government in England, to avoid a similar situation,
granted a single licence to a group of manufacturing companies,
which formed the British Broadcasting Company. In 1922 this
company, upon the granting of a Royal Charter, became the
'Z British Broadcasting Corporation (B.B.C.), formed as a monopoly
responsible to the British Parliament, and financed partly 4 from public funds and partly from a receiver licence tax.
The B.B.C. broadcast three separate networks with different
styles of programme and also established transmissions at short wave bands for information dissemination (propaganda) purposes to foreign countries. Other countries also established short wave broadcasts.
The first public demonstrations in Australia of wireless
(radio) telephony were given in 1919. Commercial broadcasting commenced in 1923 and stations were soon operating in state capital cities. The Australian Broadcasting Commission was formed by an Act of Federal Parliament in 1932 to operate the stations which the government had purchased in 1929. An overseas service is operated by the A.B.C. in addition to metropolitan and country networks.
Early radio stations used amplitude modulation (AM) to effect communications. This method has the properties that the radio frequency bandwidth is directly proportional to the audio bandwidth, the total power transmitted varies with modulating amplitude, and the method is prone to interference - 42 -
from other signals. Another method, called frequency modulation (PM), was introduced in 1940, following the work 5 of E. H. Armstrong in 1936. This method has constant total transmitted power and suffers much less from interference than AM, and because the radio frequency bandwidth does not depend directly on the audio bandwidth, increased fidelity can be obtained without altering the channel bandwidth. However, the channel required by FM is much larger than by AM, so transmissions are made in the very high frequency (VHP) band.
For this reason the range of transmissions is limited and FM has not prospered in the commercial field until recently.
FM lends itself to high fidelity use, and with quadrature modulation methods can transmit stereophony, so its use is increasing, especially in the U.S.A.
2.2 WIRE BROADCASTING
The use of transmission lines to distribute a broadcasting programme predated radio, since the techniques of line telegraphy and telephony had been developed in the last quarter of the nineteenth century. Broadcasting demonstrations were given in European cities in the 1880’s and in 1895 the Electrophone Company began to distribute a programme to subscribers using the national Telephone Company c lines." The system did not show much development because of a lack of good quality loudspeakers and amplifiers. Further development occurred after World War 1 using the equipment - 43 - developed for radio communications. The major difficulty of wire broadcasting lies in the distribution of the signals. Distribution methods have included private lines, telephone lines and electric power mains cables, and both direct audio transmission and modulation onto a carrier have been used. Distribution at audio frequencies has the problem of arranging the selection of one of several alternative programmes. If telephone lines are used then a selection device could be installed at the 7 telephone exchange to enable selection to be made. If private lines are used either each programme must be separately cabled, or the companies must co-operate to allow selection at a common point. 0 Carrier frequencies between 62 and 140 KHz have been used , and this allows several programmes to be carried on a single line. One attraction of carrier methods is the possibility of sharing the use of mains distribution cables or telephone lines, although there are problems of line attenuation and frequency response. Also the subscriber's equipment is more complicated, although a radio-type receiver could be used to 9 detect the signals. Wire broadcasting has been used increasingly in recent times to supply ’’background" music in offices, restaurants and similar buildings open to the public. The method has the advantage that it is relatively secure from accidental or deliberate interference. - 44 -
2.3 STUDIO OPERATIONS AND EQUIPMENT
2.3.1 Studio Development
In the 1930*s British studios were designed acoustically and equipped as single purpose studios, in contra-distinction to American studios which were ’’live-end dead-end” acoustically designed for multi-purpose use. 10 B.B.C. studios commonly had only one microphone and control equipment and contained one artist, so that productions with a variety of segments, such as drama, would be spread over several studios. Rehersals were difficult to control because of problems of communications and 11 sound-programme monitoring. On the other hand amplifying equipment was concentrated in a central control room, which enabled distribution of d.c. power using bus-bars, and simplified maintenance procedures. 1 2 The use of a.c. mains as the power source for amplifiers was introduced in 1938. However, centralisation meant that feeds from the studios to the control room carried low - level signals which were susceptible to interference, and the interconnection of chains of amplifiers caused volume variations when two 1 3 microphones were faded together. The emergency situation caused by World War II forced studios to be widely separated and self-contained. Hastily constructed rooms were fitted with portable O.B. equipment mounted in standard bays, which could be constructed simply and with minimum delay.^ After the war the trend of the general- purpose, self-contained studio continued, with desirable - 45 -
characteristics being: 1 5
(a) self-contained,
(b) facilities as flexible and comprehensive as possible,
consistent with economy,
(c) standard framework which allows different arrangements for various studio sizes and types, (d) adequate spare equipment,
(e) operational simplicity and comfort, (f) ease of maintenance.
The combination of central control and single-purpose studio also led to difficulties in the broadcasting presentation of items. Production staff were remote from the control centre,
so any emergency was in practice handled by engineering staff. To correct this, a new system called ’’continuity working” was 1 6 developed in 1938-39, and introduced before the war ended. The system consisted of a two-room suite, manned by a presentation official (announcer) and an engineering operator, and acted as the focal point for items forming the station’s programme. The direct control wielded by the announcer enabled a strictly time-scheduled programme to be presented, which allowed other stations to participate in networking (i.e., to re-broadcast selected items as a part of its own programme). For foreign-language broadcasts to other countries, small studio-suites similar to continuity suites were developed.
Operational methods differed from those of domestic services because of discontinuities between items. These were caused by - 46 - language changes and alterations to transmitter frequency and aerial direction.
2.3.2 Technical Equipment
Until recently, B.B.C. programme-item routing to transmitters had been performed by three methods:
(a) Before 1940, by banks of relays,
(b) During World War II, by plugs and jacks (or patchcords), 17 (c) Post-War, by telephone uniselector switches.
Banks of remotely controlled relays, formed as cross-points in a two-dimensional array, proved to be reliable provided regular maintenance was performed. Relay switching systems are economical even though the numbers of inputs and outputs are large if the number of simultaneous "through" connections is 1 s small. However, with the rapid growth and dispersion of studios and transmitters during the war, the relay system became impractical because of the sheer bulk of the equipment and the short supply of relays, so a temporary system of plugs and jacks 19 was introduced. These provided complete flexibility at low capital cost, but were untidy and uneconomical in operating staff 20 for large installations and were superseded after the war by uniselectors.
The motor uniselector is really a multi-pole switch which connects either eight or sixteen wires (poles) to any one of fifty ways (used either as outlets or inputs), or alternatively other combinations of poles and ways can be used. - 47 -
The switch operates when triggered by driving itself from a
"home" position to the outlet that has been "marked" electrically. Uniselectors are economical in both cost and space. They are reliable and do not need holding circuits, so if a power failure occurs the selections are not lost. The poles can be used for programme, telephone and cueing circuits which are switched simultaneously. There is no possibility of double selection or of stopping at an unmarked position, and the selected position can be positively indicated for 21 confirmation purposes. Disadvantages are that they are noisy when hunting, slow (since sequential) and show variations in contact resistance. Regular maintenance adjustments are recommended. Uniselectors have been used for source pre-selection and destination route-switching. A very intricate system was installed in the Overseas Service of the B.B.C. and used a timed automatic system to switch between 150 sources and 130 destinations (this is discussed in section 2.4). In addition to item production and source-to-destination switching, a third function called monitoring is performed by broadcasting operators. Monitoring is the critical examination of certain parameters in the broadcast and assists two technical functions: the setting of programme loudness level, and the maintenance of technical quality. The original form of programme loudness meter was the volume meter, a meter with specially designed characteristics and a defined unit called the "volume unit" (VU). The meter measures the energy in the - 48 -
sound wave and gives a reliable indication of loudness,
although its insensitivity to rapid peaks allows a tendency 23 toward channel overload and distortion. Between 1934 and
1933 the B.B.C. developed a peak programme meter which
indicated the magnitude of rapid peaks rather than "mean 24 syllabic" power. This unit has been adopted by the B.B.C.
Both peak and volume unit (W) meters are used in Europe, while
the VU meter is extensively used in the U.8.A. and elsewhere.
Quality monitoring is performed either by an estimate
based solely on the operator’s judgement, or by comparison
between the signals at two points in the broadcasting chain.
It is a tedious operation and the standard of monitoring varies
considerably. Hence attempts have been made to reduce the
amount of human monitoring required, by using automatic
comparison and sequential monitors. Automatic comparison can
be performed directly between two signals provided the
characteristics and sensitivity of the tests are carefully weighted. A typical use would be to compare the "off-air"
signal (i.e., the transmitted signal received and demodulated) with the signal received from the source. If an imbalance is
detected an alarm signal to the maintenance staff is sent.
Another method tested by the B.B.C. for use at remote points
involved the sending of two signals along the transmission line.
One is the normal signal, the other a code which is modulated on to an out-of-band carrier. The code represents the characteristics sampled at the source and is compared with those - 49 -
25 received at the remote point. In practice the main form
of automatic monitoring performed to-day is the programme-
failure monitor, which detects a period of low-level sound.
In cases where monitoring need only he intermittent, for example,
where one source feeds several transmitters each feed can he
sampled sequentially and presented to the operator or monitor
for comparison. Sequential monitoring has been used
particularly with programmes of fixed format, such as overseas
services, where selection of lines to he monitored can easily
he automated. In this installation a single operator monitored
the programme fed to eighteen destinations from six sources by
sequentially listening to each point for five seconds. The
total cycle time was within ninety seconds. Sequential
monitoring can be used to reduce monitoring costs and strain on
operators provided a reduced standard and a time delay in
noticing a fault is acceptable.
2.3*3 Current Trends
The tendency of studios to he multi-purpose appears to he
continuing, even to the extent of sharing large orchestral
studios between sound and television broadcasting. Recently
constructed studios fall into three categories: the large for
orchestral and variety shows, medium to small for spoken word items such as drama or talks, and small booths which are operated singly or in pairs, for continuity work.
The increasing utilisation of F.M., stereo broadcasts and 50 -
wire distribution (e.g., com. ..unity antenna TV) gives scope for
more broadcasters and increases the chances that minority tastes 27 will be served. Stations are likely to be more narrow in the
fields covered, and this tendency would give a more formalised
presentation, possibly with less critical reference to time.
These attributes are more amenable to automation techniques
than the ’’disc-jockey" style, high tempo presentation used at
present.
In networking operations regional stations appear to be
broadcasting a greater proportion of local material, providing
a balance of the projection of the lives of people in the region
against the "polished, artificial sophisticated" production of a po national centre. ( This tends towards decentralisation of
broadcasting operations with major centres supplying mainly
news and prestige items. Advances in technology have led to the use of solid state
and encapsulated reed relays in switching systems. These have
advantages of improved reliability, no need for regular
maintenance adjustments and lower costs due to the packaging of
integrated circuits used for control and signal circuits.
2.4 AUTOMATION SYSTEMS
Automation systems have been introduced both into sound
and television broadcasting. A large majority of these have been television orientated because of the relatively fixed format of presentation. This is used mainly to link pre-recorded 51
packaged items and is not so time conscious as sound broadcasting.
The main limitation on the development of automation systems has been the state of technological development, particularly in materials. With the development of integrated circuit technology and ferrite core storage, cheap and reliable memory and controller units such as small digital computers have become available. The current price of ferrite core memory is about five cents/bit, and small digital computers are less than $5,000.
Another important development assisting automation development has been the introduction of simpler methods of computer programming, such as high level languages (e.g., FORTRAN).
The earliest units were simple sequencing devices which used switches or punched paper tape as the storage medium. The first "home-built" units were tested about 1957. Commercially produced systems are continuing to be marketed with price tags of, for example, $3,000 for the controller alone2^ and $40,000 30 for a complete station production system^ including short announcement and long duration reproduction equipment. With the advent of cheaper, more reliable digital computers, stored program controllers using computers with magnetic drum, disc 31 and core storage*^ were applied to broadcasting control.
Development has taken two paths: small units for continuity control, and very large systems which also perform resources allocation and real time control of item production planning and preparation, using "Program Evaluation Review Technique"
(PERT) methods. 52 -
2.4.1 Hard-Wired Sequencers One of the earlier hard-wired systems was developed by the B.B.O. for its external sound service studios at Bush House, and commenced operations in late 1957. The use of automatic switching was simplified since the overseas programmes are scheduled for possible switching at "cardinal" quarter-hour intervals (i.e., hour, half-hour etc) only, and also the programmes for each day in the week remain unchanged for some months. The switching elements used were uniselectors, those routing the signals being controlled by a second set of uniselectors called "marking code selectors", via groups of relay stores. Special sets of metal contacts called "combs" which strap desired connections were inserted between the inlet tags of the selector. This pre-selected a group of relays so that the required route switch was marked for the next quarter- hour change. Each comb covered a quarter-houi’ interval, after which time the "wipers" were advanced one step to the next comb. Two papers which discuss general aspects of sequencing systems appeared around 1959-60. Tharpe considered the application to American television stations, its influence on the automation of non—technical areas such as sales and accounting, and the punched paper tape method of schedule storage. Partington-^ outlined a system using punched paper storage for scheduling information and a clock system which detected time co-incidence between the schedule and standard - 53 - time and decoded the characters to execute the desired operation* A notable point concerning papers which describe particular installations is that improvements are geared to advances appearing initially in the computer field. A switching unit designed in 1957 involved the use of rotary switches as preset-storing units, since low-cost memory was not available.Two years later a proposed design used beam switching tubes as memory devices. These stored the next six events, entered by the operator, and the unit sequenced through these when triggered by a clock or item
"end” cue.^° /mother novel memory unit used about 1962 incorporated a system of pinboard inserts similar to those used on analogue computer patch-boards. The complete automation system, which allowed a sixteen event sequence in a "break" initiated manually, cost at the time about $6,000* The use of EDP storage techniques such as hollerith (IBM) cards and one-inch wide punched paper tape was reported early in 1964. The preparation of the programme schedule on cards by a TV station traffic department involved 300 cards per day and one man-hour of card punching. One effect of automation reported was the need to make operations, such as replay machine pre-roll time more consistent.'^' With the punched tape input relays were used to store each next-event preset transferred from the tape. The continuity instructions coded on the tape included 39 automatic fading and special visual effects. In Australia - 54 - two television stations have employed automatic master control switching facilities. TEN channel 10 which began operations in Sydney in 1965 uses an eight event store, with each event in the station-break sequence initiated by end of item cues from the machines ArU Station AW channel 4 in Albury uses a ten event store. The hardware uses RTL integrated circuits and the system was placed into operation in May 1967. 41' Two recent installations in G-erman sound broadcasting stations are those at Norddeutscher Rundfunk (N.D.R.) and .Deutsche Welle. The N.D.R* automatic programme-continuity suite system (ASMOS) began planning in 1964 and entered a preliminary stage in 1967.'42 Central control is by permanently-wired control logic with an internal ten-event store fed as events are processed by a punched paper tape containing the whole day’s schedule. Control is time- synchronised by an electronic clock. Deutsche Welle designed an "automatic mechanical continuity unit" (ASM), five of which were placed in service between 1965 and 1967. The unit uses mechanical switches for storage of the next ten events, and relays for control logic. Transitions between items are keyed by a "sequence-switch pulse" and clock-timed switching pulses start or stop programmes. From the mechanical design an electronic unit (ASE) was developed and entered into service in 1969. Schedule input is by keyboard or punched tape reader.^ Programme monitoring and dynamic-range control is also automated ~ 55 -
As well as the internally developed systems described above, several manufacturers in the U.8.A. have marketed automation systems for the smaller commercial stations typical of the American broadcasting system. Commercial suppliers have developed cue-controlled reel-to-reel tape machines and continuous-loop cartridge carousel (multi-cartridge) machines.^
Some companies which have automation systems on the market are
’’Broadcast Products”, ’’Gates”, ’’International Good Music” and
’’Schafer Electronics”. To take an example, ’’Schafer Electronics” were working on the remote control of transmitters in 1958 when the company commenced work on automation equipment.
Developments of sub-sonic (25 Hz) cueing for switching and random-access storage of broadcasting material by high speed 45 searching and cueing were included in later designs.
Then, as cheaper digital computers came on the market broadcasting manufacturers and users began to consider their use for the smaller stations.
2.4.2 Stored Program Continuity Control
Early in 1961 A. B. Ettlinger of CBS Television Network published a paper on the use of digital computers for switching control/"' He suggested that the introduction of a computer would give two improvements: random-access memory and a stored set of instructions for the control unit. The former would allow modifications to schedule data without physical changes to hardware, and the latter could be programmed to scan several - 56 -
future events for pre-roll operations. Computer hardware available included a "desk-top” model costing $50,000 and using a rotating magnetic drum as memory. Reliability was held to be good, and included the use of parity checking.
In a later paper Ettlinger described a specific installation in a CBS television station, which began 47 automated switching operations at the start of 1961. The station break switching sequence was manually initiated by reference to a count-down time display, although an absolute time display was also available. Manual control was achieved by three controls: "switch", "hold" and "discard" Buttons. The installation used a process control computer manufactured by the TRJ Computers Co., and employed a 5,000 word (24 bit) memory drum. This could be expanded to 8,000 words although only 20fo was used for item data, storing 220 events expandable to 1,400. Data entry was by means of a special keyboard which entered characters for storage first to a display for checking, and then storing. Using the "3earch-entry" mode schedule data could be corrected. Bttlinger has recently described a non continuity use of computers, in the control of television 48 studio lighting patterns. This uses a "mini" computer and digital-to-analogue converters to control lighting dimmer circuits. The data display and entry method utilises an alphanumeric (TV-like) display and a light pen for entry.
Applications of computers to broadcasting have been extensively explored in Japan. The Japan Broadcasting Corporation (N.HJEC.) has introduced a very large system
(discussed in the next section) and commercial firms have developed units for smaller stations. One such system was reported by three staff-members of IECE and ITE Japan at the
London Conference on Automatic operating of Broadcasting equipment in November 1966. " They have designed a computer controlled system called APC-361, which uses a "flexowriter" keyboard-entry and printing unit (with paper tape reader and punch attachment) and a T0SBAC-3300 computer. The memory consists of 4,096 words of 24 bits (+ parity) of core storage and two magnetic drums (each 7, 168 words). One drum is used for schedule data, the other for back-up of the main core memory. The flexowriter is used to place the schedule on punched tape. This is read intermittently into main store, processed into "programme" and "cue" events and stored (up to twenty events) on the drum. Operations are synchronised to "true-time” by reference to a digital clock. Several North American companies such as C.D.L., Ampex and Schafer Electronics have used small digital computers to provide automation facilities similar to those described for hard-wired sequencers. At a recent symposium on automation and computers in broadcasting two contributors, from the B.B.C. and the S.A.B.O., described computer controlled sound broadcasting. The B.B.C. is developing an automated system which includes a computer, for its External Services studio centre at Bush House. This will replace the automatic switching system which was described in - 58 - section 2.4*1 (page 52). There were three reasons for replacements: (a) timing constraints necessary for the switching system were not accepted in the studios,
(h) system physically too large, 50 (c) equipment was not sufficiently reliable. Hence manual operations were re-instated. In designing the new system, minimal time segments were defined as quarter- hour modules. The uniselector switcher was replaced by a code-bar system. The new control system has two parts. The first comprises a Digital Equipment PDP-8 computer with 4,096 twelve-bit words of memory and a magnetic drum. This is used to store and edit the schedule data, entry being either by punched tape or a keyboard/display terminal. There are two data stores used, one keeps the basic schedule pattern which is c anged only four times/year, and the other a "current-day" store. Items with data of uncertain validity are specially marked as "liable-to-change". If the mark is not cancelled by a time five minutes before the broadcast, a warning is given. The second part is the advance control unit which stores the data for the next switching-event and sequences through the operations during a two-second pause in transmission. Thus the computer itself is not "on-line" but acts as a readily accessible storage device which passes switching data to the sequencer. Monitoring is performed by programme-failure detectors, and in the case of breakdown manual control is used. - 59 -
The only equipment duplication is the clock system. Because of the large number of sources and destinations a studio occupancy test also interrogates the studio staff to confirm that the computer has selected the correct combination of source and destination. If confirmation is not made five minutes before the broadcast, an alarm is given.
The South African Broadcasting Corporation (S.A.B.C.) has at present in service a hard-wired automation system 51 which contains six different formats, Bach format can contain up to twenty four sequences, set up by thumbwheel data entry.
Sources include tape replay units with sub-sonic (25 Hz) cueing and a ‘'speaking clock" using two announcement tapes advanced alternatively by the Master Clock. The main limitations of the system are the inflexibility of the hard wired formats and the production of commercial "spot-tapes". The commercials are recorded in sequence on a long tape, separated by 25 Hz cues. This process is time consuming and boring, so consideration is being given to computer control of commercial-spot production and presentation. The system being developed for production of commercials uses an IBM 360/50 to prepare the in-sequence recording off-line. The system uses a seven-track recording system and the computer produces replay instructions on punched tape. The presentation system consists of selecting sources in strict sequence (apart from studios) with new items cued directly from 25 Hz cues rather than by computer control. The computer control system concentrates on - 60 -
schedule preparation and advertising-spot production rather
than continuity control.
Computer control of television continuity operations is 52 55 54 55 also projected and several papers 9 9 9 report
investigations and system designs. The designs use small
process control computers together with punched tape for
schedule entry, and keyboard/display terminals for amendments.
2.4.5 Large Systems
N.H.K. commenced computer development efforts in 1961*
The first process implemented was of the batch type which
handled process payroll and accounting. At the same time the
development of an all-embracing on-line system controlling
planning, production and transmission presentation for sound
and television was commenced. The system, called "TOPICS",
began operations in November 1968. N.H.K. states that
computerisation has saved 5,000 staff, out of a present total
of 16,000 (representing a cost saving of $US 15,900,000).^°
Opposing this, the development and installation of TOPICS took
550 man-years and development cost $US 2,000,000.^
N.H.K. operates two television and three sound networks, with a total of 26 television and 55 sound studios. The aim of TOPICS was "to increase the efficiency of programme productions and to utilize at a maximum all the resources 58 necessary for such production." It was hoped that the staff requirement would be minimised by eliminating the need for - 61
MMAl COMPUTER
AMSTER FILE
SCHEDULE file /t£soO&.c&£- fKLLOCATiOAj File
AHHOUXCliZ FUM CAMLHf\MAH SlUp/O EUE/FdeC OS ERE/ElE/Z PZMG-NdfZ MATRIX SOU ED effects MAX
LE6£f\10 ! -----> infop^mation > FfLo&RAmz
fit £- f FUNCT!OHM D/MM OF "TOPICT 62 - written memoranda. To perform this TOPICS contains two major tasks: (a) Scheduling Management and Allocating Resources Technique
(SMART), (b) Automatic Broadcast Control System (ABCS).
The associated hardware consists of an IBM 360/50 computer with two magnetic drums and two discs, and an IBM 1800 process control computer with two discs. These units are duplexed for reliability. 59 Figure 2-1 gives an overall picture of the TOPICS system.
SMART is used to register production items, follow progress and report conflicts or deficiencies. Producers register their items using one of 220 alphanumeric terminals and indicate preferences for staff and equipment which are available. SMART maintains files on each item for resources allocation and PERT/critical path method processes. Problems are reported to system managers in the Broadcasting Control Centre (BCC), Eight graphic display units are used to convey information in tabular and graphic form. BCC staff can also assume control of the broadcasting presentation system if an emergency arises. START operates within the main (IBM 360/50) computer. Schedule information for the current-operations is passed when demanded every ten minutes to the transmission control system,
ABCS.
The ABCS is centred at the Technical Operations Centre
(TOC) and controls production and transmission operations - 63 -
TAPE AECOdPEi
MAt/S - e>'T/v v. ------> MlSi/ON MATK/X
LOCAL STATION \N£WS N£Ai7/£S
LZcAErzo : --- > IN AO mat I Oh! ^ P&O&ftAMMt:
A Ns. 2-2 FUNCTIONAL P/AG-faM OF "ABCS* — 64 — equipment. Figure 2-2 shows the functional control maintained by the IBM 1800 process control computer,0^ Facilities provided inclu.de identification testing and automatic cueing and commencement of television and sound broadcasting items.
The switching matrix can be controlled automatically and manually, and if the data link to the 360/50 computer fails then the schedule can be entered using a keyboard at TOG. Two points of interest are the sound tape replay units and the failure protection arrangements. The tape units are a joint HHK-CB3 development and consist of two vertical replay decks positioned either side of a vertical stack of tapes on spools of special design. Thus continuous service is provided with each tape automatically loaded and threaded. A total of 42 tapes can be carried in the stack. aluminium foil is placed on the tape to provide an end cue, and as the tape speed accuracy is only - 0.2/ the replay machines are set to run fast. The computer inserts fill-in material to cover the period between the item's conclusion and the commencement of the next. To protect against computer failure both the 360/50 and 1800 are duplicated, the stand-by units operating in duplex with the operating units. Change-over between 1800's takes three seconds, while 360/50 is a slower manual operation taking ten minutes. Hence the ABCS stores schedule data for ten minutes ahead. To avoid breaks in power supply NHK has taken extensive precautions. Two separate mains supplies with automatic change-over are used, and these are "backed-up" with - 65 -
a 11V/ generator which automatically starts and reaches operating speed in three seconds. In addition the 360’s are
supplied through a separate motor-alternator set to give surge-free supply. The IBM 1800*s, which are more critical
for on-air control, are fed from a static supply with floating
battery of one hour capacity.
The latest development by bHK is a financial reporting and analysis system : "FINMS." This gives trends of revenue, spending and other management data. Forecasts are made of the effects of particular management decisions. However, at r a this stage FINAHS must be regarded as experimental• 66
CHAPTER 2 -__REFERENCES
1 REGINALD LESLIE SMITH-ROSE, "Marconi, Marchese Guglielmo," Encyclopaedia Britannica, (edition of 1962), XXIV, p 869*
2 RALPH BROWN; WALTER FIRTH LANTERMAN, "Broadcasting : V, U.S. System," Encyclopaedia Britannica, (edition of 1962), IV, p 210. 9 "Golden Anniversary of Broadcasting," Electronics Australia, July 1970, p 11. 4 JOHN CHARLES WAL3HAM REITH, 1ST BARON REITH; GORDON G. A* WINTER, "Broadcasting : VI. BRITISH SYSTEM," Encyclopaedia Britannica. (edition of 1962), IV, p 214. 5 RALPH BROWN; WALTER FIRTH LANTERMAN, loc. cit., p 212. 6 T. WALMSLEY, "Wire Broadcasting Investigations at Audio and Carrier Frequencies," The Journal of the Institution of Electrical Engineers, Vol. 87 (No. 523), July 1940, P 76. 7 Ibid., p 77. 8 E. L. E. PAWLEY, "B.B.C. Sound Broadcasting 1939-60," The Proceedings of the Institution of Electrical Engineers, Vol. 108, Part B, No. 39, May 1961, p 292. 9 WALMSLEY, op. cit.. p 88. 10 BURTON PAULU, British Broadcasting. (Minneapolis : University of Minnesota, 1956), p 137. 11 H. D. M. ELLIS, Studio Engineering for Sound Broadcasting, ed. J. W. GODFREY, (London : Iliffe, 1955), p 85. 12 Ibid., pp 54, 67. - 67 -
13 P. WILLIAMS, "The Trend of Design of Broadcasting Control Rooms," The B.B.C. Quarterly, Vol. II, Bo. 3, October 1947, p 186.
14 PAV/LEY, op. cit., p 284.
15 H. D. ELLIS, "Studio Equipment : A New Design," The B.B.C. Quarterly, Vol. I, No. 1, April 1946, p 21.
16 R. T. B. WYNN, "Continuity Working," The B.B.C. Quarterly. Vol. I, No. 4, January 1947, p 185.
17 H. D. M. ELLIS, Studio Engineering for Sound Broadcasting, p 105.
18 R. D. PETRIE and J. C. TAYLOR, "Programme Switching, Control, and Monitoring in Sound Broadcasting," B.B.C. Engineering Monograph, No. 28, Pebruary I960, p 7.
19 PAV/LEY, op. cit., p 285.
20 P. AXON and 0. H. BARRON, "Planning and Installation of the Sound Broadcasting Headquarters for the B.B.C.1 s Overseas and European Services," Proc. I.E.E., Vol. 107, Part B, No. 36, November I960, p 486.
21 W. H. G-RIN3TED, "The Motor Uniselector and the Technique of its Application in Telecommunications," Proc. I.E.E., Vol. 96, Part III, 1949, p 419.
22 PAV/LEY, loc. cit.
23 H. D. ELLIS, op. cit., p 166.
24 Sir NOEL A3HBRIDG-E, "Broadcasting and Television," Joum. I.E.E., Vol. 84 (No. 507), March 1939, p 382. 68 -
25 H. 13, M. ELLIS, op. cit,, pp 169-171. 26 H. D. M. ELLIS and J. C. TAYLOR, "The Design of Automatic. Equipment for Programme touting and Sequential Monitoring," The B.B.C. .Marterly. Vol. VI No. 4, Winter 1951/52, pp 241-242. 27 ROSS II. P-RISH, The Political Economy of Broadcasting, (Armidale : University of New England, 1968), p 13. 28 J. GOATMAN, "Regional Broadcasting," The B.B.C. Quarterly, Vol. II No. 3, October 1947, p 164. 29 G. DEXTER RAYMOND, "Integrated Circuits for Low-Cost Automation," Broadcast Management/Engineering, Vol. 6 No. 9, September 1970, p 32. 30 JOSEPH D. COONS, "Y/OHI : Fully Automated Talk Station," BM/E, Vol. 6 No. 9, September 1970, p 29. 31 W. R. CRAIG, "The Stored Program Control of Line Signalling Relay Sets in Telephone Networks," Australian Telecommunication Research, Vol. 2 No. 2, November 1968, p 30. 32 PETRIE and TAYLOR, op. cit., p 21. 33 JAMES B. THARPE, "Television Program Automation," I.R.E. Transactions on Broadcasting, Vol. BC-7 No. 1, January 1961, pp 39-41. 34 G. E. PARTINGTON, "Automation of Television Programme Switching," Journal of the Brit. I.R.E., Vol. 20 No. 3, March I960, pp 181-196. 35 RAYMOND W. RODGERS,."A Preset Switching System," I.R.E. Trans. Broadcasting, Vol. PGBC-13, February 1959, pp 1-4. 36 F. CECIL GRACE and CHARLES E. SPICER, "Automatic-Sequencing Equipment for Television Operation," Journal of the Society of lotion Picture and Television Engineers, Vol. 70 No. 3, March 1961, pp 150-155 - 69 -
37 ARTHUR FREILICH and SaUL MAYER, ‘The "Step" System - A Unique, Low-Cost TV Automation System,1 IEEE Trans. Broadcasting, Vol. BC-9 No. 1, February 1963, pp 16-23# 38 M. REED, "All-Day Automated Programming Utilizing IBM Card Prestorage," IEEE Trans. Broadcasting, Vol. BC-10 No. 1, February 1964, pp 19-23. 39 JOHN T. MILNER, "Some Advanced Technical Features of the New ii/BAL - TV Facilities," IEEE Trans. Broadcasting, Vol. BC-10 No. 2, December 1964, pp 63-65. 40 H. IIRZWINSKI, "Automation of Master Switching Systems," E.B.U, Review, Part A-Technical No. 97, June 1966, p 111. 41 T. R. R. JONES, "An Automatic Master Control for Television Stations," paper presented to TREE 12th National Radio and Electronics Engineering Convention in Sydney on 23rd May 1969, (document : Abstracts of Technical papers, p 100).
42 3. PONNIG-HaUS, "Automatic Programme-Continuity Control for the N.D.R.*s Sound Broadcasting Service," E.B.U, Review, Part A-Technical No. 122, August 1970, pp 164-172. 43 0. ROESSLER, "The Present State and Future Development of Automation in the Deutsche Welle," E.B.U. Symposium on Automation and Computers, Hamburg, October 1970, (document : Tech. 3092-E, pp 122-135). 44 GENE HOSTETTER, "Automated Radio Broadcasting," db, February 1970, p 19. 45 CURTIS GARNE3, "Broadcast Automation," International Broadcasting Engineer, No. 35, August 1967, p 262. 46 A. B. ETTLINGER, "Digital Computers for Television Automatic Switching Control," IRE Trans. Broadcasting, Vol. BO-7 No. 2, March 1961, pp 29-36 - 70 -
47 Idem, "CBS-KNXT Computer Control System for Program Switching,” Jo urn, of the SIvIPTE, Vol. 70, No. 9, September 1961, pp 691-695* 48 Idem, "New Applications of Computers in Television Programme Production, ” E.B.U. Symp. Broadcasting; and Computers, Hamburg, 1970, (document : Tech. 3092—E, pp 108-113). 49 CURTIS GAANES, "Automatic Programme Control and Colour Television in Japan," International Broadcasting Engineer, No. 34, July 1967, pp 220-221. 50 A. M. WOODBRIDGE, "Control of Switching in the External Services of the B.B.C.," E.B.U. Symp. B/C and Comp., Tech, 3092-E, p 139. 51 D. G. H. IvULLS, "Automation and Use of Computers in the S.A.B.C.," E.B.U. Symp. B/C and Comp., Tech. 3092-E, pp 148-157.
52 J. GUILLERIvHN, "Automation of a Television Continuity Suite," E.B.U. Symp, B/C and Comp.. Tech. 3092-E, pp 250-256. 53 J. S. SANSOM and N. W. GREEN, "Computer aids in Television Signal Switching," E.B.U. Symp. B/C and Comp., Tech. 3092-E, pp 258-269. 54 G. LAHANN, G. 3CHADWINKEL and H. WELCHAUSEN, "The N.D.R. Computerised Television Installation (COIvIPAS)," E.B.U. Symp. B/C and Comp.t Tech. 3092-E, pp 272-281.
55 I). M. B. GRUBB, "Automation in the B.B.C.*s Television Service," E.B.U. Symp. B/C and Comp.. Tech. 3092-E, pp 284-288. 56 H, MATSUURA, "General Approach to the Use of Computers in Broadcasting - Improvements in TOPICS," E.B.U. Symp. B/C and Comp.. Tech. 3092-E, p 14. - 71
57 Ibid,, p 19.
58 G-. J. LISSANDRELLO and NOBUO Mil, • n h k "topics", • . Telecoimnunication Journal, Vol. 36—XII, December 1969, p 667.
59 NHK PUBLIC DELATIONS BUREAU, "The NHK* s on-line programme production and information control system," E.B.U. Review, Part A-Technical No. 115, February 1969, P 58.
60 Ibid., p 41.
61 MATSUURA, op. cit.. pH. - 72 -
CHAPTER 3
PRESENT TECHNICAL OPERATIONS SYSTEMS
3.1 METHODS OP ITEM PRODUCTION 74
3.1.1 Live Sources of Material 74 3.1.2 Methods of Item Storage 76 3.1.2.1 Disc Recording 77
3.1.2.2 Tape iiecording 79
3.1.2.3 Digital Recording 82 3.2 METHODS OP PROGRAMME ITEM PRESENTATION 83
3.2.1 Single Unit - Broadcasting Stations 83 3.2.2 The Centralised Network 85
3.2.3 The Decentralised Network 87 3.2.4 Combinations of Network Types 89 3.3 CONSTRAINTS ON TIMING OP OPERATIONS 90 3.3.1 Item Timing 90 3.3.2 Planning of Operations Schedules 91 3.3.3 Clock Systems and Time Synchronisation 92 3.4 TECHNIQUES OR ITEM PRESENTATION 94
3.4.1 Time UnsynchronisedSequential Cueing 94 3.4.2 Time Slot Y/orking 95
3.4.3 Exactly Timed System 96 - 73 -
3.5 MANUAL SYSTEMS OF OPERATION 97
3.5.1 The Two-Man System 99
3.5.2 One-Man Operator Method 100
3.5.3 One-Man Announcer Method 101
CHAPTER 3 - REFERENCES 102 - 74 -
CHAPTER 3 PRESENT TECHNICAL OPERATIONS SYSTEMS
3.1 METHODS OF ITEM PRODUCTION
An item of information material which is to he broadcast
is generated in the first instance by human agency. The material can either be transmitted immediately, which is called "live broadcasting", or can be stored for later re-production by using recording techniques.
3.1.1 Live Sources of Material
The production of an item for immediate broadcast can be performed within a specially designed room, called a studio, or can occur at a location remote from the studios and transmitter.
Most broadcasting stations have several studios which are generally situated at a single location close to a centre of population and commerce. The transmitter is quite often situated remotely from the studios at a location giving good propagation of the radio signal. The studio itself is constructed with acoustic properties suitable for broadcasting speech or music and is provided with accurate clocks and displays of other information which enables the station*s programme of items to be presented smoothly*
One of the principal advantages of live broadcasts is that the item duration can be varied by the people participating in the generation of the item. Those who - 75
control the proceedings of the item are known as announcers or commentators; the former generally repeating previously prepared announcements, while the latter describe events and offer an interpretation of them*
Also, announcers normally broadcast from a studio whereas commentators, particularly on sporting events, broadcast from remote locations, these items being called
"outside broadcasts"*
An announcer can monitor the lapse of time and listen to the passage of other items in between his own announcements*
Thus he can decide to make last-minute changes in announcements and item material to adjust item broadcast durations, to give pleasing presentation of the station*s programme. Often extra staff such as production assistants and technical operators are assigned to the studio to pass visual or aural cues and to control signal levels*
The commencement time and duration of an outside broadcast are more difficult to control, which complicates the planning and operation of a station’s programme.
The difficulties occur since:
(1) the item is usually an official proceeding or an event
provided for public entertainment, which are
synchronised to an independent time-table,
(2) outdoor events are subject to changes in weather
conditions,
(3) communications between commentators and the presentation - 76 -
staff at the studios are often inefficient. The live studio
production also has disadvantages. One is that the studio is occupied at the time of broadcasting, at least, and often for a considerable period beforehand to reherse the item. As many items are broadcast during the evening or early morning to cater for certain sections of the potential
audience, this means that "talent” (that is, participants in the item) and supporting staff have to work at abnormal hours. This problem can be overcome by using a method of storing the item’s electrical signal for later re-production and
broadcasting. This system is especially useful when the participants such as public officials or celebrities are available at particular times only*
3.1.2 Methods of Item Storage Storage techniques are used to enable the generation of an item at a time different to the actual broadcasting time. In addition, the recorded item can more easily be exchanged with or sold to other broadcasting stations than live items, with which communication difficulties and standard time difference can interfere. One difficulty associated with recording for later use is that reference by announcers to topical events, such as the local time could be misleading. Time calls could be recorded, but difficulties of
synchronisation with actual time during replay are likely to occur - 77 -
Desirable characteristics of a recording system are:
(a) high fidelity of reproduction of acoustic properties
and time durations,
(b) immediate access to any instant of the recording,
(c) simple editing and copying methods,
(d) robust (ie non volatile) so many replays can be made
but medium can be erased of the item for re-use,
(e) multi-signal storage on a single copy of recording for
stereophony,
(f) small recording copy size for ease of transportation,
(g) simple recording and replay equipment*
Signals can be recorded either in continuous signal form
or in digital form* Digital methods encode, at a specific
sampling rate, signal parameters such as instantaneous voltage
into a multi-level system for storage using binary memory units.
The most common forms of continuous recording systems are:
(a) modulation of a groove cut in a rigid disc,
(b) orientation of magnetic dipoles in grains bonded on a
base of thin, narrow tape.
3• 1 •2.1 Disc Recording
In disc recording the recording medium is a platter, or
thin disc, of vinyl, acetate or similar material. The
electrical signal is converted into a lateral mechanical
displacement of a groove cut in a spiral on the face of the disc* To reproduce the signal the lateral displacement is - 78 -
detected by a stylus whose output is a voltage proportional to the displacement. The storage is permanent, so the unit is not re-usable for another item. Also, one or two stages of casting (or stamping) from the master are used, before copies are finally made.
Disc recording has the advantages of permanent storage, reasonably robust copies and rapid access to any location on the spiral groove. The size compared to recording time is satisfactory and the fact that the disc forms a single rigid unit means that storage and transportation is simple. The groove length remains constant, so duration values are repeatable if the turntable speed is constant.
Disadvantages are that recording and replay equipment is fairly expensive and skill and care are needed to operate the equipment, both to cut the disc and also to set-up for replay into a broadcasting item. The problem in replay is to "cue” the disc at the desired starting point (not necessarily at the commencement of the groove) and to achieve a "fast-start” with no pitch changes. This is usually achieved by lifting the disc clear of the turntable. Normally editing and copying is not simple. However the British Broadcasting Corporation uses a system of "Direct Cut Lacquer" disc recording, utilising lacquer-coated aluminium discs.^ This enables rapid editing of items onto a disc and immediate replay, but the recording is not permanent and the fidelity varies with position along the spiral groove. - 79 -
Two channel stereophony can he recorded on discs by recording one signal in each of the two walls of the groove.
Each ’’track” is cut at 45° to the plane of the disc and so is orthogonal to the other track. In this way it is hoped that intermodulation is minimised. Groove width varies when the signals are in phase and the depth varies when they are 2 out of phase. Only two signals can be recorded and the recording cutter and reproduction stylus are costly and delicate to ensure no cross-modulation.
To summarise, disc recording is possible, although lack of editing facility and cost of recording equipment have limited its use. For the mass production of items for commercial sale, disc usage is very extensive, since the disc is robust and cheap to copy in large quantities.
3.1.2•2 Tape Recording
In tape recording the signal is converted into a magnetic flux which changes the orientation of magnetic dipoles bound in a thin film onto a plastic (or similar material) base.
The base is cut into a narrow strip or tape, typically i inch wide, and about 0.001 inches thick. This process was patented by J. A. O’Neill in the U.S.A. and F. Pfleumer of Germany about
1927, and was developed by the Magnetophon company of Germany during the 19 30 * s.^
To produce the recording the tape is passed through the magnetic flux developed across an air gap in a magnetic circuit - 80 -
(the recording ’’head”) at a constant speed. Reproduction
is effected by means of similar "head” which converts the
variations in magnetic flux caused by orientation of dipoles
into voltage by induction. Several separate signals could be
recorded along the length of the tape as separate ’’tracks”,
although the wider the track, the greater will be the signal
strength compared to any backgound noise or "hiss” (signal/
noise ratio). The tape is usually wound on a plastic or
aluminium reel in lengths of 200 to about 7000 feet.
Recently short lengths of tape have been fitted into self-
contained cases, either as reel-to-reel feed of the tape, or
as a continuous coiled loop. The former type is called a
cassette, the latter a cartridge. Only short durations, up
to 15 minutes are available at present and the fidelity is
less than the larger reel-to-reel systems.
Tape possesses several advantages over disc recordings•
Tape has good fidelity, simple copying and editing methods,
is re-usable, and uses simple recording and replay equipment.
Several tracks (multiple channels) can be easily recorded, or several different items can be recorded in parallel and selected by changing the replay head position. Operators of recording and replay equipment do not need special skills.
Disadvantages of tape are:
(a) access is sequential only (that is, the tape must be
wound from one reel to another until the desired location
is found); 81
(b) storage is relatively volatile, since stray magnetic
fields can erase the pattern of dipole orientations;
(c) the tape base, whilst having the advantage of flexibility,
suffers in the longitudinal direction from elastic and
inelastic deformations.
Point (c) causes variations in the fidelity of reproduced pitch and in item duration. Elastic deformations vary with the tension exerted on the tape during replay. Inelastic deformations, usually stretching, cause permanent changes and often occur with incorrect braking of tape movement from reel to reel. Similar variations in pitch and duration can be caused by varying the tape speed, which suggests a means of correcting tape length variations. By recording a ’’mark” at specific time intervals along the recording track, the replay speed can be adjusted until the reproduction gives a similar time interval between marks. Somewhat similar methods of recording controlling signals on a separate track are used on television tape-recordings but usage is rare for audio
(ie sound)-only recordings, since the cost of control is proportionally higher for the simpler audio-only recording.
It is possible that simpler methods using time interval marks recorded on the main track at sub-sonic frequencies can lead to simpler control systems, and studies are being carried out in this direction.^ 82
3.1.2.3 Digital Recording
Digital recording involves the sampling of the signal voltage at a certain rate. The sampled value can then he converted into a number selected from a scale of numbers.
The number, which generally consists of binary digits, can be stored in discrete storage cells. Methods have been developed which reduce the number of digits necessary to store the information of instantaneous voltage. For example, the change in voltage from one sample to the next can be 5 monitored, rather than the voltage itself. If the sampling rate is high enough the bandwidth of the audio signal will restrict the variation in voltage to "up or down one level".
This reduces considerably the number of digits needed, but introduces the danger that an error is propagated in time and the algebraic sum of errors becomes important. This effect occurs because the parameter sampled is relative, not absolute, and the error can be reduced by re-establishing absolute values periodically.
The digital numbers can be stored mechanically, either by modulating grooves on a disc or by perforations in tape or cards, or magnetically on tape or disc. Other types of storage are available, such as ferrite cores, thin film, sheet c ferrite and superconductive memories. At present, cost and bulk preclude the use of these latter, except possibly short recordings of a few seconds only, and continuous signals can be recorded with less operations on disc or magnetic tape. - 83 -
Digital recordings could be used, however, if further processing of the signal were required for some purpose (as, for example,
’’slow motion” in television).
3.2 METHODS OF PROGRAMME ITEM PRESENTATION
A broadcasting station can operate as a single
independent unit or can share items by linking with other
stations. This linking is called networking, and it offers a saving in production costs, although it imposes constraints on the methods of presentation.
3*2.1 Single Unit - Broadcasting Stations
The simplest broadcasting station consists of a single studio and a transmitter. The studio itself would contain microphones, disc and magnetic tape replaying units. It is necessary to be able to connect these signal inputs to the transmitter and preferably to be able to mix the signals and fade them slowly. Variable attenuators are used to achieve this, the composite signal being fed to the transmitter.
Other signals which are also controlled are those conveyed by transmission lines from outside broadcasts.
Larger stations contain several studios, some of which are designed for a specific purpose such as music production, drama, or announcements. It then becomes necessary to switch the line feeding the transmission between these sources of programme items. This switching is called, source switching - 84 -
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and is often performed within a small announcement studio, called a continuity suite or transmission booth* It is the task of the occupants of the suite to ensure that items follow each other smoothly.
In a single independent station, there is no reason, except for the convenience of listeners, to synchronise the operation of the programme to ’’standard time”. The major constraint on operations is that conterminous items join smoothly, that is, without overlap or cutting, and without periods of silence.
3.2.2 The Centralised Network
When two or more stations whose areas of potential listeners are disjoint exchange items by considering the source station as an outside broadcast, then a network is established. The item being relayed must fit neatly between other items, so synchronisation of operations, using a common standard of time, is required. Although this need not be the official, or geographical, standard time this is usually adopted to comply with audience needs.
A relatively simple form of networking utilises a centralised system, with one station acting as the source of items relayed to the network. The source, or ’’master”, station does not receive items from other member stations so its generation of material must be continuous. In this sense its operations are little different to those of the — 86 —
-/£ 5-He) DECENTRALISED NETWORK - 87 -
single independent station, with the "slave" stations receiving a copy or "split" of the master’s transmitter feed.
However, each slave station has to combine the network-generated items with its own programme. This demands a knowledge of the durations of its own items and a knowledge of the commencement times and durations of the network-originated items.
To assist in the control of this type of network a method of signalling is often used. For instance a short duration musical tone or a gong-sound can be used to cue slave stations to join or leave the network. Combinations of tones of different pitch, sounded sequentially can signal to specific stations. Incidental items which can be included or deleted at the final moment before transmission are used to adjust programme time synchronisation.
Figure 3.1 (b) illustrates the centralised network arrangement.
3.2.3 The Decentralised Network
When more than one of the network member stations can assume control (that is, becomes the "master") the network becomes decentralised. The dependence of smooth presentation on accurate timing of operations becomes more critical since an error at one of the possible master stations affects the programmes of all the others. This requires very good communications between controlling centres, with error-free channels and minimum delays, or alternatively, strict adherence 88 -
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to a switching time-table which gives absolute priority to the next scheduled item. In any case, the planning of the programme of each member station must be more detailed and prepared earlier than in previous network types.
Figure 3*1 (c) illustrates the decentralised type of network arrangement.
3.2.4 Combinations of Network Types
Both centralised and decentralised components can be found in large broadcasting networks. An example occurs in the system of three networks controlled by the Australian
Broadcasting Commission (A.B.C.). The geographical concentrations of population in Australia give rise to National stations with considerable autonomy located at each state capital city. Two networks, featuring "light entertainment" and "cultural" programmes, are generated for city-metropolitan listeners using the decentralised network system. Audiences in country regions can listen to local A.B.C. stations which are slaves in a centralised system. The network-produced items fed to a regional station are selected at the master station in the capital city either from one of the two metropolitan network programmes or from a separate third network programme consisting of rural type items. Thus another stage of switching, called network switching, is introduced into the master station operations, to supply slaves from one of three networks. In the A.B.C. the signalling system - 90 -
between stations consists either of gongs, or previously prepared word cues from announcers. Three gongs of different pitch are sounded sequentially for network
(decentralised) changes and one single gong for regional
(centralised) changes.
Figure 3.2 shows some of the programme feeds to A.B.C. stations•
3.3 CONSTRAINTS ON TIMING OF OPERATIONS
To obtain a smooth flow of items periods of silence between items should be kept to a minimum. This is also desirable from a commercial operations viewpoint, since time is the commodity which is sold to advertisers. Modem practice allows one or two seconds of silence at most between
items, for switching operations. To obtain such precision three pre-requisites are necessary:
(a) accurate production duration and stable reproduction
duration of items to be broadcast;
(b) detailed planning of operation schedules of each station
to ensure switching time co-incidence;
(c) a common time standard, with a method of synchronising
station clocks.
3.3.1 Item Timing
The required accuracy of item timing is that of - one second per time interval between switching operations. In - 91
live productions this can he achieved by the announcer who
can insert or delete material to cause adjustments of about
1 30 seconds. However, recorded items can prove troublesome.
Both disc and tape replays are afflicted by incorrect measurements of item durations, either in stop-watch operation and reading or in transcribing figures. This problem is often compounded by the fact that some items have indefinite
starts and endings which causes the person timing the item
to make personal judgement of the duration. Also, variations
in replay mechanism speed from one machine to another cause
compatibility problems.
In addition, magnetic tape is not stable in its length.
This can be corrected by using costly feedback control methods but is not generally in use in sound broadcasting studios.
Operational techniques have been developed to cope with these timing problems, and will be described in the next section (3.4)
3.3.2 Planning of Operations Schedules
The task of the operations schedule is to convey
information regarding:
(a) destination of item;
(b) source of item to be broadcast;
(c) means of identification of the item;
(d) time of switching operations;
(e) duration of item.
Point (c) is not necessary information for the source-destination - 92 -
switching operator; however, the same schedule is usually used hy the source controlling operators. Item identification is a useful means of detecting errors in source or switching operations. If the duration of items is only known approximately then some other system of identification of item completion must be specified. A "cue” such as a gong-sound, or a particular phase of music or spoken words is usually indicated in the operations schedule. Planning of switching events should take into consideration problems of local geographical time (for example the two hour time difference between Eastern and Western Standard Time) and use of daylight-saving time.
3.3.3 Clock Systems and Time Synchronisation Desirable features of a station operations clock system are (a) power supply independent of common, or "mains", supply; (b) all station clocks give the same reading; (c) system can be synchronised to an external reference. Modern time pieces are usually either driven mechanically or by an electric motor, although electronic counters and digital displays are now available. Mechanical clocks have self-contained sources of energy, so are independent of "mains" supply. However, apart from non-linear mechanical coupling of vibrations (in pendulum clocks), the clocks also operate independently. The chance of operational errors being caused by non-time coincident clocks puts the mechanical type at a - 93 -
severe disadvantage compared to other master-slave systems.
Common domestic electric-powered clocks use a time
reference the period of the alternating mains voltage. Over
a long period (of, say, 24 hours) the mains frequency averages
50 Hz quite accurately, to one part in 40,000 ( - 2 seconds).
However, at any instant during the period the error can be
substantial. For example, an error of 0.5$ in frequency for Q two hours, which can occur late at night, would cause clocks
to be in error with astronomical time by more than 36 seconds.
This is unsatisfactory since the present-day criterion is -
one second, at worst.
An alternative means of driving electric clocks is to use a central "master" oscillator which either supplies a
continuous wave at the correct frequency, or supplies pulses
at the correct repetition rate. Both these methods are
incremental in nature, so errors which develop in a slave clock will continue to show and will add algebraically until a re-synchronisation of the slaves occurs. This can be incorporated in the design; for instance, the "minutes" can be next after a period of an hour, although preferably at a time when operational events are unlikely. Digital counting and display systems do not suffer from this problem since the absolute reading is displayed each second. A difficulty of these displays is that announcing staff use the circular display of "Analogue" clock to estimate the period of time remaining before some action is needed. The method of estimating is - 94 -
similar to the "pie crust" method of drawing graphs for
illustrative purposes. To change to digital clocks would
require considerable re-education of announcing staff, whose
operations are controlled by estimations of the lapse of time.
To allow distant stations to operate as a network their
time standards must be synchronised. This is normally
achieved by using a common reference such as observatory time
which in Australia is distributed by the Australian Post Office,
Other references are standard time signals broadcast by radio
station WWV in America or the Post Office station VUG- in
Australia,
In conclusion, the clock system usually adopted employs a
master oscillator or pulse generator which has an accuracy of
10 to 100 milleseconds per day and has provision for correction
of time for synchronisation,
3.4 TECHNIQUES OF ITEM PRESENTATION
The central problem of presentation is to have each item
commence on time, and yet achieve a smooth delivery of the material. Several methods of operation can be used, the
complexity depending upon the precision of timing required,
3.4.1 Time Unsynchronised Sequential Cueing
In cases where synchronisation of presentation to a time
standard is not required (such as in the independent station) the next item can be initiated by a signal generated at the - 95 -
conclusion of the previous one. These cues can take the
form of tones which, with magnetic tape replays, can he
recorded on the tape itself. The cue can either he on the
programme item track as an out-of-hand (frequency, time,
or amplitude) signal or can he recorded on a separate track.
The tone can he detected hy the operator for manual
intervention or it can he used to automatically start the
replay of the next item.
The method is rarely used in a manually operated station as reasonably frequent synchronism with standard time is desirable, to attract listeners. It does, however, lend itself to automated control of operations.
Since the times of switching operations are not predictable, announcements of present-time must either he given "live", or generated hy a time-advanced recorded announcement system similar to the “speaking clock" operated hy the Australian Post Office.
3.4*2 Time Slot Working
The method of time slot working enables the commencement of major items to he synchronised to standard time while still allowing the item duration to he indefinite. This is accomplished hy allocated to a major item a period of time, or
"slot", which is somewhat longer than the item’s nominal duration. The difference between the slot and the item’s actual duration is filled hy substituting optional-use material. - 96 -
This can consist of a number of short announcements of definite duration such as programme publicity or advertisements, but must include an item of indefinite duration, such as a passage of music or a short period of silence. If silence is used it can be inserted at any convenient switching time.
However, it is preferable to arrange that a musical fill-in item reach its conclusion, for pleasant effect. This is obtained by using a piece of definite duration and commencing at the time which gives the desired time of conclusion. The switch from major item to music is not performed until the end of the item is signalled. This cross-over, which is effectively the indefinite commencement time of the music, compensates for the variation in major item duration from the nominal value.
The intra-slot operations can be controlled by using the time unsynchronised sequential cueing method. This is applicable since the large possible variation of the major item is compensated by the indefinite duration of the fill-in music and since the durations of the short announcements do not appreciably affect timing.
3.4.3 Exactly Timed System
If the durations of all items in the station programme were stable and measured accurately, then it would be possible to initiate switching operations by reference to the system clock only. Such a situation is possible since feedback control - 97 -
systems can control reproduction from tape sufficiently
accurately and skilled announcers can control the live item duration "by stretching or compressing speech delivery.
However, success depends very much on each link in the chain of time measurement, planning, production control and reproduction control being correct that the chance of failure is high. Thus the system could be said to be inherently unstable although "equilibrium" is attainable.
In an automated system, a method of testing the rate of progress of "item-time" (i.e., protime) might allow replay speed adjustment to correct item durations. Thus the items could be forced to conform to the operations schedule. This idea will be considered later.
3.5 MiAHTJAI SYSTEMS 0? OPERATION
Manual presentation operations are carried out in small rooms called continuity booths. The original form of continuity working required two people per programme of items developed, an announcer and a technically trained operator.
Recent advances in equipment design, such as cartridge and cassette replay units, have enabled continuity to be maintained by one person only. This tends to reduce the number of on-air staff but also tends to regiment operations. - 98 -
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FF CM C£/vTTAl TO C£A/TPAL SWITCH/rV G- POOM S' 3.5.1 The Two-Man System The continuity suite for two-man operation consists of two booths, one being an announcer’s studio, the other a q control room for the studio. A simplified diagram of the facilities of the suite is shown in figure 3.5. The announcer’s duties include the making of introductory remarks for ensuing items, giving time announcements and issuing cues for remote stations to join or leave the network. He quite often controls the switching of sources to the continuity suite output (receiving cues from remote stations) and cues and starts disc replays. To assist him he is generally provided with a clock, "on-air" warning lamp and an indication of destinations actually connected to the suite. He is also able to "pre-listen" or monitor the signals on in coming source transmission lines and the suite output. The technically-orientated operator controls the volume, or "level", of the items being broadcast and selects or arranges the selection of signals from remote sources. His main function is to monitor and correct the technical quality of material being produced. With advances in tape replay machine construction, these units have been installed in the suite rather than remotely located, and the operator usually loads and controls the operation of these. Two-man operation is used for presentation when there are a large number of short items to be presented sequentially. The most complicated instance is the sporting result sessions 100 - broadcast at the weekends. This production requires split- second decisions on acceptance of next source, most of which are remote and so could have communications problems. Alternative sources of items must be ready to cater for delays in outside broadcast events and mobile equipment failure. Whilst one person must be in command (the announcer), sometimes two or three extra people are required to handle source selection and communications. 3.5.2 One-Man Operator Method In many cases the major items are of considerable duration and the intervening presentation items consist of short introductory remarks and local time calls. The two- man system is wasteful of staff as only one is needed to monitor the quality of the item. The time slot method of operation can be used to advantage since the short announcements can be pre-recorded during normal office hours on cartridges and the operator can use a multi-cartridge replay unit in addition to the reel-to-reel tape units. The multi cartridge replay units have automatic cueing, by means of a separate track for tone signals. Once a cartridge begins playing the tape will run until a ’’stop” cue is reached. This cue is located at the start of the next announcement. Cartridges with sufficient fill-in music and with standard types of apologies can be held to cater for failure in item production. The time slot method enables the non item-creative 101 operator to control time progress in order to synchronise with externally timed events such as switching of networks or broadcasting of standard time signals# 3.5.3 One-Man Announcer Method Sometimes the continuity of programme requires a continual contribution of announcements, but activity is not so intense as to require two people. In this case the announcer can be given sole control of the presentation and automatic volume which occur due to the assembly of different items into the programme. Such cases are often called "disc jockey” programmes because of the number of operations performed by the announcer in rapid sequence. Often the presentation is really the production of an independent item but is often performed in a continuity booth. The method allows frequent time announcements to be made and so is used particularly in the mornings for "breakfast” type items. CHAPTER 3 REFERENCES H. BURRELL HADDON, High - Quality Sound Production and Reproduction, (London : Iliffe, 1962), p 168-172. Ibid., p 252. WELBY EARL STEWART, "Tape Recording, Magnetic," Encyclopaedia Britannica (edition of 1962), XXI, p 798A. J. B. HILLER, University of New South Wales, Personal Communication, (October, 1970) J. A. GREEFKE3 and K. SIEMENS, "Code modulation with digitally controlled companding for speech transmission," Philips Technical Review, Vol. 51, No. 11/12, 1970, p 338. CORDON B. DAVIS, An Introduction to Electronic Computers, (New York : McGraw-Hill, 1965), p 491-493. Gr. J. JOHNSON, "Frequency Measurements of the N.S.W* Electricity Supply," Proceedings I.R.E.E. Australia, Vol. 26, No. 12, December 1965, p 394. Ibid., p 392. F. M. SHEPHERD, "The A.B.C. Sydney Programme Centre," Proceedings of the I.R.E. Australia, Vol. 20, No. 8, Aiigust 1959, p 457-458 103 - PART - B AUTOMATION SYSTEMS FOR BROADCASTING - 104 - CHAPTER 4 THE CASE FOR AUTOMATION 4.1 THE TASKS IN A BROADCASTING- STATION 105 4.2 TYPES OF AUTOMATION SYSTEMS 106 4.2.1 Hard-Wired System 106 4.2.2 Stored Program Control System 108 4.3 RELIABILITY OF AUTOMATED SYSTEMS 111 4.3.1 Availability of Controlling Equipment 113 4.3.1.1 Reliability and Maintainability 113 4.3.1.2 Assessment of Automation Equipment 118 4.3.2 Reliability of Signal Transmission 121 4.4 DEFICIENCIES OF THE MANUAL SYSTEM 121 4.5 ADVANTAGES AND DISADVANTAGES OF AUTOMATION 123 CHAPTER 4 - REFERENCES 125 105 - CHAPTER 4 THE CASE FOR AUTOMATION 4.1 THE TASKS IN A BROADCASTING- STATION The operational tasks which are performed in the presentation section of a broadcasting station are: (a) identification of each item or part of item; (b) starting and stopping of replay equipment; (c) switching to connect sources with destinations (transmitters); (d) fading of volume or "mixing" (superimposition) of signals using variable attenuators; (e) preliminary setting of signal path parameters such as gain or frequency response; (f) the control of signal levels during broadcasting; (g) the detection of deterioration in item technical quality or catastrophic failure, and taking remedial action; (h) scheduling usage of reproduction equipment for best utilisation; (i) modifying schedule of programmes to remove timing mis-synchronisation; (j) testing new operations schedules for inconsistencies; (k) routine testing of equipment not in immediate use; (l) logging of events. Of these, items (b), (c), (d) and (g) require immediate action while (f) is dynamic but incorporates some delay in reaction, (a), (e) and (i) usually have a short period during which time action can be taken; the other items are serviced 106 as low priority tasks. The starting of replay machines must take account of any time needed for the machine to reach correct operating conditions. This is done by starting the machine at an earlier time (pre-rolling) after having re-cued 4 the recording to allow for the extra time used. 4.2 TYPES OF AUTOMATION SYSTEMS The differences between automation systems lie in the methods of forming the control signal paths which implement the designed functions of the control system. Two methods frequently used are: (a) permanent, or ’’hard-wired", connections; (b) stored program of control instructions. 4.2.1 Hard-Wired System The control system takes inputs and feedback from outputs, reaches decisions according to specified control laws and provides appropriate outputs. In the "hard-wired" system the interconnections between the controlling units (which can consist of analogue amplifiers and logic gates) and between the controllers and inputs and outputs are made by permanent joints. This has the advantages of being reasonably cheap to construct, for systems with only a few separate tasks, and makes the system reasonably secure from inadvertent connections or manual interference. The major disadvantage of this method is that it is 107 - difficult to modify the control system in order to cure operational difficulties which appear after commissioning of the system. Usually the automated control system will have to he removed from service for an extensive period whilst modifications are made. The reversion to manual control of operations will introduce a number of presentation errors because of the loss of skills caused by lack of practice. One of the most expensive units of the automated system is the memory unit, and so financial limitations often restrict the storage size, which reduces the number of operational events scheduled within the system. Most systems use memory devices such as electro-mechanical relays, flip-flops or ferrite cores to store the information relating to the next few (for example ten) events. Each event could consist of the reception of a cue signal, starting of next item and switching the new source to the output of the station. As each event is executed the stored events are effectively advanced towards the execution apparatus, and the store for the event just completed can be reloaded with new data for the event to follow the last one stored. In simpler systems the data is entered manually by an operator, whilst larger systems make use of punched cards, punched paper tape, less expensive but relatively slow access magnetic drum, or some combination of these. One of the frequent short-comings is that after some experience it is found that insufficient events are held in storage because of changes in presentation methods. 108 - Another problem is the detection and correction of errors in the data stored in the broadcasting programme schedule, and the modification of data caused by last minute changes in schedules. Inconsistent data could possibly be detected by logical tests, but this requires complicated hardware for possibly little return. All data could be checked manually as it enters the next event store, but this requires an operator whose duties the automation system should have annexed, except in the simple system of manual entry. Last minute changes could be introduced either by manual intervention into the next events storage, or by punched cards, whose sequence can be re-arranged. Finally, the addition of extra tasks to the hard-wired control system involves costs which are roughly proportional to the size of the extra tasks. Hence no particular advantage occurs in building large scale hard-wired systems. 4.2.2 Stored Program Control System In this method the controlling devices consist of the logic units, such as gates and adders, which form part of the circuitry of a digital computer. The required interconnections between these units and the external environment of broadcasting equipment and data input devices are made by means of binarjr numbers stored in a bank of memory units. The numbers are interpreted by logic circuits as instructions on completing the interconnections. Because of the read and write 109 - facility of the memory units the numbers can be modified during the controlling operations, and this allows the control of processes to be dynamic, rather than fixed* The control system design is converted into a sequence of instructions, called the "program”, which is stored in the computer’s memory bank. Broadcasting schedule data is also stored in another part of the memory bank. The outputs of the system consist of digital values, which could be used to control switches or converted to continuous voltages by digital-to- analogue converter equipment. Inputs could be numbers from analogue-to-digital conversion of continuous voltages or digital data such as condition of switches or coded information concerning switching or other tasks. The major advantage of the stored program control system is that the interconnections, which are "soft" stored as instructions in memory, can easily be changed to accommodate modifications to the broadcasting presentation system as a whole. The control of presentation need be interrupted only during the actual transfer (read-in) of the new control program into the computer’s memory, since testing of the new system could be carried out "off-line" on a similar type of computer (which could be hired for this purpose, if necessary). With fast read-in units no interruption of actual tasks need occur since the change could be performed during the broadcast of a long item, and the system restarted as though a power failure had occurred 110 - By "off-line" testing, errors in the new control program can he discovered and eliminated without the need for reversion to manual control for extensive periods. Another advantage of stored program control is that the operational schedules are stored in a similar manner to the control program. This usually allows a large space of memory, for a considerable number of events, and enables modification of the storage to correct errors or make last minute schedule modifications. The control program which enables schedule modification can carry out some grammatical and consistency tests, and can immediately display the modified schedule to allow new errors to be detected. Slower access memory, such as magnetic drums or discs, can also be included in the control system to greatly extend the memory accessable to the stored program for the holding of data for operations. The main disadvantages of the stored program system is that of initial cost of equipment and development of control program. The minimum cost of a small computer and memory, suitable for broadcasting system control, is about $A 5,000 and design and development staff need to be conversant with the instruction system of the particular model of computer. Thus the use of stored program methods for a small station*s automation system is not warranted, unless equipment costs can be balanced against savings in staff, and development costs spread over several buyers. This latter is possible only if all the broadcasting systems to be automated are similar in nature. In large 111 broadcasting stations, where the introduction of any automation system requires extensive analysis of operations, the initial costs of computer and stored program development are small compared to the continuing advantages of easy modification to the system* Another disadvantage is that operators are removed a further stage from the scene of operations because decisions are stored in the program* System and hardware faults are difficult to analyse and rectify and operators need a higher level of training since the stored program method is more difficult to comprehend than a hard wired system. Thus operators involved in system maintenance require greater ability and more training* 4.3 RELIABILITY 01 AU10i..ATBjJ SYSTEMS Broadcasting presentation operations consist of a sequence of events which initiate activities, synchronised to a prepared time scale. To perform these operations successfully an automated system must be reliable and this requires: (a) the controlling units to be in correct working order, (b) cueing signal interception, (c) error free transmission of digital or analogue control and data signals, (d) schedule data to be accurate. In addition it is desirable that the subsystems of the broadcasting system perform tests on each-other1s output for 112 COMPONENT RELIABILITY (%) pic. 4-1 mmm of sews common 113 - accuracy so that wrong information or inappropriate action can be corrected. 4.3*1 Availability of Controlling Equipment The ideal situation is that the automated controlling system be available for operation at all times. This can be approached only with the penalty of high financial cost so it is useful to consider what availability is obtained from hard- wired and computer controlled systems, and the methods of increasing it. Availability is related to reliability and maintainability. 4.3.1 .1 -Reliability and Maintainability The reliability ( R ) of a device or system is its freedom from failure. It is expressed as a fraction and is related to the average probability of failure. For non- maintainable equipment, system reliability can be defined as the product of the individual reliabilities, R, of the i components when tney are connected in series. Figure 4-1 shows the change in A , with the number of series connected *— o 2 components. For example, with 100 components each of 99% A, R is only 36.8^. To improve R^ one can either: (a) increase A of each comj)onenf, (b) introduce redundancy so that failure of one link does not cause failure of the system. Redundancy is obtained by the parallel connection of two or 114 - N = HVlA&Efk OF CoMPoa/F A/TS cC c <4J V CDMPOU/ZNT ££i/A£lLITY (%) FtGA-Z RELIABILITY OF CiEMML CMIMMIE 1 Z AWHIM OF COMfOFFA/FS c X K —. 10 zo ■'J '-U << So § 100 £ (S) 100 99 9 7 9e 95- COMPONENT HBUASlLiry (%) F/0.4-5 EFFECT OFMLMMEMK EMI ZEL 115 - more components. Thus the system will not fail until all the components in the parallel link fail. Figure 4-2 shows 3 R of redundant components as a function of component R. The redundant components can either be directly paralleled or substituted by switching. However, there would be a certain unreliability associated with the switch. Also, of course, a permanently wired parallel component must fail in a way that does not interfere with the operation of other parallel components. Failures can be considered to be of two types: catastrophic and non-catastrophic. The former is one in which an abrupt change of some important parameter to zero or infinity occurs. The latter occurs when the parameter is not stable, but drifts outside some tolerance value.^ Non-catastrophic failure is important because the cumulative effect is very marked when large numbers of componeiits are used. This is indicated in figure 4-5 which shows Ro for non-catastrophic failures, with ~s 5 linear superposition. It is also interesting to consider the force of mortality of a device, i.e., the probability density of the device failing at a certain instant of time. As shown in figure 4-4 (page 116) mortality force distribution has three distinct zones. When time is small "infant mortality" pre-dominates but falls sharply. Then a long period of time passes with constant rate of mortality due to "chance" failures. As the operational time becomes large the device wears-out and the rate of malfunctions increases. The force of FORCE OF MORTALITY FORCE o f MoYTAl./T/ A F!0. FIO. itffAtir 4-F 4-4 MouTkury A m'S REM chmce TIMS OF OF moat 116 WRULITY MAIN A - utv FEN wem ANCE FORCE - out mokt * iit / 117 - mortality during this "wear-out" period can be modified by the application of maintenance to the device. Maintenance at this period can be of two types: preventative and repair, the former being the replacement of components before malfunction occurs, the latter after malfunction, Figure 4-5 shows the applicability of maintenance and the effect on c mortality force. Maintainability ( M ) is the capability of an equipment to be returned to an operational status within a specified time. Alternatively, for depot maintenance it is associated with 7 overhaul within a specific percentage of unit cost, depends on the repair time, or "downtime" which is affected by design decisions, maintenance policies and technician requirements. Downtime is the sun of detection, diagnosis, correction and verification times.0 Such things as circuit accessibility and interaction between circuit parameters influence diagnosis and correction time. Maintenance policy on whether failed components are repaired or discarded also affects downtime and maintenance costs. Modular replacement of a sizable unit of the system improves M but raises the cost of spares. Availability ( A ) can be considered to be dependent on R, M and effectiveness of supply of spares ( 3 ), i.e., A = f ( R,M,S ) ...(4*1) Using Mean Time Between Failure (MTBF) as a measure of A, Mean Time To Repair (MT1R) for M, and Mean Time Waiting for 118- Spare (ITTWO) for 3, A_ can be expressed as:'y IlTBE - = LfBHVifCTR-f-L^dd ...(4.2) Thus for high A it is required that MTBf1 be large and MTTR and RTU3 be small. To some extent however, R and U interact. If R is optimised to increase MTBR it could well be at the expense of D which shows an increased MTTR. An example of this is the case of integrated circuits which are highly reliable but restrict accessibility to some points in the circuit. 4.3.1 .2 Assessment of Automation Equipment Automation equipment includes digital and analogue computers as specific entities, components such as integrated digital circuits and relays, and connection methods such as wire wrapping. Analogue computers have in the past suffered mainly from d.c. drift in amplifiers. This can be considered as a non cat as trophic failure although the situation is at least reversible, i.e., drifts in opposite directions tend to cancel. The use of solid state devices with higher voltage ratings and improved temperature stability have reduced this problem. Digital computer manufacturers claim values of MTBF of many thousands of hours, typically about 7,500, whilst the MTTR is a "few minutes". Using these figures availability is almost unity, but since the particular operating conditions of the test are not stated the figures should be viewed with 119 - suspicion. Reliability decreases if the equipment is often disturbed, as happens during the development phase of automation systems. Interface connections are often changed, modifications and further accessories are added to the computer installation. However when the automation system is in an operating condition the "environment" improves and better R can be expected. The other aspect of A, namely H, is a different story. One of the effects of increasing R has been to reduce M. Integrated circuitry and the multiple operations performed in a single computer "step", make it difficult to observe changes in parameters. Another problem is that it is difficult to arrange the computer architecture as a series of similar modules. Hence the method of carrying spare modules is very costly, and the question arises as to whether the parts should rather be invested in a second computer. The use of redundancy increases A, since both reliability and aids for maintenance will increase. Redundancy can take the form of a second unit which normally performs low priority tasks. Alternatively the supporting units can be run in duplex so that discrepancies in operational results can be detected. with digital control equipment such as in telephone exchanges, 10 * 11 duplication is common, and recourse to triplication as the ideal "majority rule" system 1 2 has been suggested. Some relationships with R and M using maintained system reliability with redundant units have been discussed by Homyak. 13 120 Extremely reliable relays are now available, in the 7 form of reed-relays which have lifetimes in excess of 10 operations. The current rating of the contacts is low, but this would probably not pose any problems in broadcasting installations. For heavier currents, up to five amps, mercury wetted reed relays are available, and these have o lifetimes better than 10 operations. Integrated circuits have also proved very reliable, once the rather high infant mortality period is passed. The method of preventative maintenance becomes useless since failures are of the pure chance variety rather than wear-out. To summarise the position for broadcasting automation, high reliability of components and systems can be had, but maintainability is a problem because of the time synchronisation dependence of broadcasting operations. A redundant system of two computers is advisable since changeover can be performed between the periods of high activity at switching times. Unless well-trained computer maintenance staff are on hand, which is unlikely in a broadcasting environment the MTTR could be quite high. Hence a dual-processor and memory system with an non-call" or maintenance contract for the occasions when one unit is down, is the best solution. The construction of interfacing and broadcasting control equipment using modular techniques and similar circuit designs is important for system M. 121 4-0*2 Reliability of Signal Transmission Most of the signals sent between the automation and broadcasting systems are digital in nature. The signals direct contact closure and sense operated states as well as exchanging numerical information. They are unlikely to suffer noise interference in the broadcasting studios, since equipment such as low-level microphone amplifiers are highly susceptible to interference and steps towards compatibility are already in force. Precautions should be taken to filter mains power supply of spikes, either using a motor generator set or an electronic regulator. Low signal level digital signals, which are found in magnetic disc and tape reproduction stages are liable to suffer interference. However, most computer systems employ parity checking as a safeguard against this. The use of parity checking with interfaces to broadcasting equipment is not worthwhile, except in cases of difficult recovery of signals, such as recovering in-band signals. 4.4 LLPIOlfHClLl OP THdl MfHUal lYSTHM Presentation (continuity) operations are required to maintain the steady flow of material for transmission. The characteristics of the programme items and broadcasting as a system impose some difficulties in implementation of the operations. These are: (a) presentation tasks are not uniformly distributed in time, 122 - so that long periods of inactivity are followed by snort peaks of intense activity, and congestion can occur, (b) failure of an item to commence, or to continue progress is catastrophic because of the requirement of time synchronisation. Manual methods of control are not well suited to these characteristics due to: (a) imperfect memory of operators, (b) physiological reaction time of operators, (c) psychological reactions of operators. Imperfect memory means that operational skills, which consist of a sequence of operations need to be learnt and continually practised to re-inforce the learning. The need to attain and retain skills in purely mechanical tasks detracts from the person*s opportunity to contribute artistically. Physiological reaction time coupled with waning skills exacerbates the difficulties of controlling intense activity periods at the conclusion of major items. What begins as a minor fault in presentation operations, can be compounded if the particular operator panics. bven in normal operations a particular station "break" might require a dozen operations to be completed in the correct sequence and at the correct time. Reaction time reduces the likelihood of success, since some operations must follow within the second. The third problem, of psychological effects includes the tendency of operators to exclude or minimise time spent 123 - on certain operations, particularly those which do not affect his local group of operatives. For example, the relay of material from one station to another, tends to cause reduced operational service (e.g., monitoring) because it has no local effect. Automated service does not have "favourites11, unless this is specifically designed into the system as a priority level, so a more balanced distribution of task servicing can be achieved. 4.5 ,u)V.hiT-G-hd aid D13 JjyAbTAGFS OF AUTOMATION The advantages of automation are: (a) operational errors tend to be reduced because of: (i) reliable response to a recognised stimulus; broadcasting system operations have been accurately specified and desired response designed into the control system, (ii) response time is sufficiently fast that congestion does not occur at the peaks of activity, (b) reduction of operating costs because smaller staff requirements occur if sufficient tasks and duties are automated, (c) costs of expansion of broadcasting operations are not necessarily pro-rata. If the computing system is not overloaded, new operations simply become extra events within the controlled operation, (d) accurate logging of events can be obtained simply. 124 - Disadvantage s include: (a) the response to new situations is unknown, (b) maintenance of the computer system could cause problems because of the lack of trained technicians, (c) item preparation must be more exact, since the automation system is intolerant of errors or omissions, (d) high initial cost, (e) delays in changes to operational procedures could occur because of the need to re-program the computer. The main advantage of automation is the tendency to reduce peak activity errors, and to carry out assigned tasks faithfully. The major disadvantage is the difficulty of adjusting computer tasks to changes in operational procedures and in coping with inaccurate time information. 125 - Ori,^: PER 4 - RHFERHj,;CES 1 ERICH FIERU3CHILPrinciples of Pliability, (Englewood Cliffs : Prentice-Hall, 1963), p 45. 2 Ibid., p 46. 3 Ibid., p 49. 4 i. A. HEY/, "Component Reliability in Post Office Equipment," Phe Post Office electrical Engineers* Journal. Yol. 54 Part 1, April 1961, p 40. 5 PIERUSCHKA, o-..» cit., p 54. 6 Ibid., p 141. 7 A. 3. COjDMAN and T. B> 3 PLPTERY, Maintainability, (Hew York : John v/iley, 1964), p 5. 8 Ibid., p 20. 9 Ibid., p 32. 10 R. W. Wiliam, J. 3. NOWAK and 1. 3. TUOI EHOKSA, "Ho. 1 E33 Maintenance Plan," Bell System Technical journal, Vol. GIII, Ho. 5 Part 1, September 1964, p 1966. 11 ■. ■ ■ m, K* S* DUHTLAP and H. R. H0PM.-:H, "Ho. 1 3 5 Switching network Fr sines and Circuits," B.3.T. J., Yol. XLIII, Ho. 5 Part 2, September 1964, p 2235. 12 J. I. LIUTZSHESH, "Using Mini-Computers in Systems Engineering," Electronic Engineering. February 1971, p 47. 13 3. J. HOEUYiLh, "Mathematical Interrelationships Between Reliability and Maintainability in Various Systems Models," I SEE I r an s ac t ions on Applications end Industry. Yol. 83 Ho. 75, November 1964, pp 413-420. 126 - CHAPTER 5 DESIGN OF A COMPUTER CONTROLLED SYSTEM 5.1 SERVICING OF TASKS 128 5.1.1 Time Slicing 128 5.1.2 Priority System 129 5.2 DERIVATION OF OPERATIONAL TIME 132 5.3 SCHEDULING OF OPERATIONS 136 5.3.1 Reasons for Schedule 136 5.3.2 Schedule Storage Methods 137 5.3.3 Servicing the Schedule 144 5.4 ITEM PRESEHTATION METHODS 152 5.4.1 Assembly Methods 152 5.4.2 Switching 155 5.4.3 Fading 159 5.4.4 Item Identification 164 5.4.5 Item Commencement Cueing 168 5.4.6 Time Announcements 170 5.4.6.1 Magnetic Tape Method 171 5.4.6.2 Rotating Memory Methods 177 5.4.6.3 Digital Random Access Method 180 127 - 5.5 THE COMPUTER AND PERIPHERALS 186 5.5*1 Central Processor and Memory Units 187 5.5.2 Character Input/Output Devices 189 5.6 REVIEW OP COMPLETE SYSTEM 192 CHAPTER 5 - REFERENCES 193 128 - CHAPTER 5 DESIGN OF A COMPUTER CONTROLLED SYSTEM The main design criteria are: (a) to ensure that broadcasting operations are synchronised to a reference time standard; (b) to ensure that the computer devotes sufficient time to each required task to complete it; (c) to establish fast, error-free data and control paths to inputs and outputs (which include the broadcasting equipment and the operations staff). The methods used to meet these are discussed in the following sections. 5.1 SERVICING OF TASKS There are two basic methods of servicing tasks: (a) by giving fixed intervals of time, called "slices”, to each task; (h) by giving each task a priority. 5.1.1 Time Slicing In this method a basic time interval is selected which is no greater than the maximum permissable time between successive services of any of the tasks. This interval is then divided into slices whose period is sufficient that the proper execution of any task is not impaired by an interruption. 129 - A particular task could be allotted several slices, and if the task is not completed during this instance of service, then its status is stored for the next entry into the task’s service routine. The apparatus necessary for time slicing is: (a) a real time clock to indicate the completion of time slices; (b) a means of detecting that a task is completed; (c) a method of storing information if the task has to be left unfinished. Time slicing has the advantage that, when the durations of the repetition and slice intervals have been fixed, implementation is reasonably simple. It suffers from the disadvantage that it is inflexible, so that service of a task with high demand could become congested, even though the computer is idle at other times. This can be alleviated to some extent by allowing a dynamic redistribution of slices to tasks during operations, dependent on demand and task importance. This leads to the idea of a priority structure. 5.1*2 Priority System The priority system offers two advantages. Firstly, it allows tasks which are considered "more important" to take precedence over others, and gain immediate access to the computer. Secondly, the more important task can retain access until its service is completed. In this way the likelihood of congestion is reduced since the tasks greater in importance acquire time from the lesser. 130 - The collection of tasks is formed into a hierarchy, with those tasks requiring immediate attention being the highest, and others with less critical interaction being lower* This gives a scale of priorities, which can be implemented by two methods: (a) the computer can search the tasks for calls; or (b) each task can interrupt computer operations to allow its request to be considered in terms of current task priority status. In method (a), a task can signify a request for service by setting a two-state storage unit to one of the states (that is, a "flag” is raised, or set). When the computer is not busy it scans each flag in turn, the frequency that a particular flag is tested depending on the priority of the task associated with the flag. The disadvantage of this method is that during the service of a task no other task can gain access to the computer. Method (b) overcomes this problem by means of a circuit which suspends the normal instruction-fetch and execute operation cycles of the computer. Some form of this circuit has been fitted to many commercial brands of computers, most allowing the option of enabling or disabling the interrupt circuit under the control of the user's program of instructions. A more simple form of interrupt circuit has only one circuit, or level, to which all tasks which can demand service are attached. When an interruption does occur the operating program - 131 must poll the task flags to locate the call, and then determine whether this call has priority over the present activity* Enabling or disabling the interrupt circuitry eliminates the disadvantages of method (a) since low priority tasks can be interrupted, but higher priority tasks which disable the interrupt, can have unimpeded use of the computer. More advanced interrupt systems provide several interrupt circuits which give multi-levels of priority rating. As an example of commercial computer design, the "PDP - 11" model digital computer built by the Digital Equipment Corporation provides four separate sets of interrupt circuits which give four levels of "hard-wired", or "hardware", priority rating. External devices associated with tasks can be connected to one or other of these levels, with connections of several units to the one level being in series form. This causes a grading of priority within the level so that the nearest unit to the interrupt circuit has the highest, and the farthest the lowest priority. When the computer is running, the central processing unit (C.P.U.) stores the current priority level of the job being executed. If a task of higher priority requests service it is allowed to interrupt proceedings and gain control. Each device has a pair of memory locations which give the memory address of the device's servicing routine of instructions, and the level of priority which the C.P.U. should adopt for the service. This latter allows the execution time priority to differ from 132 - the interrupt request priority. This "software” priority can also be modified by an instruction in the servicing program. In addition to the above, many computers have a "direct memory access" facility which allows devices to acquire short time periods during the computer*s operations, without interrupting the execution of the instructions. This enables very high speed devices such as a magnetic disc to enter (or extract) data into (or from) the memory. The multi-level priority system allows dynamic control of operations since priorities of tasks can be altered to suit changing conditions of the process being controlled. There is some loss of flexibility in the above system because a task has to obtain access via its hardware priority rating before it can modify its current rating by programming instructions. 5.2 D3HIVATI0N Off OPERATIONAL TIME There is a particular requirement for an accurate clock system in broadcasting. Operational time must be displayed at locations where manual operations are performed and must be fed to the computer in a form that allows scheduling and execution of time-initiated tasks such as programme switching. One method is to use a "real time clock" which is usually offered as an optional unit with computer purchases. This -unit is often of the Schmitt-trigger type and acts to cause an interrupt whenever a suitable change in input voltage is sensed (and the interrupt is enabled). The real time clock is 133 - commonly used in time-sharing applications, with the input being fed a sample of mains voltage. However, mains supply does not have sufficient short term stability of frequency, so its use is not desirable, except as an emergency frequency source. Instead, a crystal derived voltage with a frequency stability of one part in 10^ or better could be used, as a drift of a few milliseconds per day would be satisfactory for the broadcasting system. The periodic interruptions of the real time clock can be counted by an incrementing routine in the computer, and the ’’count” can be processed to give a ”time-of-day", or clock, reading. These digits could be used to indicate operational time in studio and continuity areas and could be transmitted either in binary form or coded (for example, binary coded decimal, or BCD). Also, a one-second repetition rate pulse could easily be developed to control the movement (i.e., to drive) of analogue (dial) clocks. A serious disadvantage of the computer generated clock system is that if the computer’s supply of power fails there is no means of determining the period of the failure. An external clock with an independent power supply, such as a battery- powered pulse generator and counter, or a mechanical clock would allow this. The electric counter would be better because of greater stability and ease of transmitting output. Thus, the complete system consists of an independently powered digital clock of high stability which has two outputs: 134 - (a) an accurate frequency signal or pulse train for input to the computer*s real time clock; (b) digital signals indicating operational time. The computer uses signal (a) to develop its own version of operational time which is used to schedule time-initiated tasks, A comparison between the computer time and signal (b) of the digital clock can be used to indicate a malfunction in one of the systems. In the event of computer failure, operational time is still available for emergency manual operations. Also, when the computer returns to service, adjustments to schedules and operations can be performed taking into account the period of time when the computer was inactive. Similar action can take place in the event of mains power failure. If the independent clock system fails the computer counting system can still be used for scheduling and can drive studio clocks provided a frequency source feeds the real time clock. This could be a separate crystal-locked oscillator, or a sample of the mains voltage. It would be necessary to have a system of initialising the time-of-day value stored in the computer’s "clock”, and also a method of correcting small variations from astronomical time (or Post Office time) that mains frequency would introduce. A problem of the clock system is to detect a malfunction or error in reading. Catastrophic failures are immediately obvious since the clocks fail to advance their readings. Also, 135 - STANDA/^O i TO k£f>£A T££ Cuock Pl>fLAy$ FIG-. 5-1 OPER!\ flcmL CLOCK SYSTEM -136- a malfunction in a circuit situated where the systems are duplicated will be shown by a disagreement in time indications* However, if the common source-oscillator malfunctions to the extent that it drifts off frequency, the error might not be noticed until faults in presentation begin to occur* Continual comparison against another local oscillator is not advisable unless the second unit has greater stability and reliability than the first. As this is likely to prove more expensive, it is not worthwhile since the second unit ought to then become the master of the independent system. One answer is to test the oscillator at frequent intervals against some external standard frequency similar to VNG or the VLF radio transmitter at North West Cape in Western Australia* By keeping graphs of readings, tendencies to drift could be noted. In the event of presentation timing faults occurring, the quickest method of establishing errors of the order of half a second or so is to compare operational time with the "speaking clock" announcement provided as a telephone service by the Post Office. A schematic diagram of the suggested clock system is shown in figure 5-1• 5.3 SCHEDULING- OF OPERATIONS 5.3.1 Reasons for Schedule A number of the broadcasting system tasks listed in section 4.1 do not demand service by interrupt or flag-setting methods, 137 - but are scheduled by the broadcasting control system user to be performed at certain times. These tasks are: (b) commencement of item replay machines; (c) switching sources to destinations; (d) programme item fading and mixing. In addition, item (a) (programme item identification) and (e) (preliminary adjustment of signal parameters) of the list in section 4.1 impose a final-call time limitation, to allow a request for manual action. If a call to perform these tasks is not received by a time of, say, three minutes before the item’s scheduled commencement time, then the control system sends a reminder to the operator controlling the source. In a similar manner a studio "test of occupancy by operator" can be instituted a short period before a previously vacant studio is to commence broadcasting. In these cases an alarm should be "sounded" if the critical time for reaction is reached. In order to recognise that service of one of these tasks is required, the computer must be able to compare a list of time values with its own internal time. This list of times, plus information detailing the task and affected operational equipment make up the schedule of operations. 5.3.2 Schedule Storage Methods The desirable features of schedule storage are that: (a) the data is compact (i.e., economical in storage requirements); - 138 - (b) a minimum of processing is needed to convert the input data format to the control system format; (c) initial entry methods and editing to modify a schedule for late changes or correction of errors is simple. There are several methods of arranging the storage of the schedule in the memory. All use the basic sequence of ordered time values, with a precision of one second required because the maximum tolerable period of silence is about two seconds. However, the methods differ in the method of defining events, the various classifications being: (a) a single list including all tasks with events defined as: (i) all tasks which require service at the one instant of time; (ii) an individual service of any task which is needed at the particular instant of time (hence the schedule could contain several references to the same time value); (b) separate schedules for some aspects within the broadcasting system. Schedules could be separate for each: (i) task; (ii) source; (iii) destination. Considering these methods in terms of the desirable features given above, (a) (i) is compact in storage and requires little processing to convert the input into a suitable form for servicing. However, the rigidity of input specification which simplifies processing makes the data entry and editing tedious - 139 - and prone to error. The alternative of a relatively free input format increases the processing needed to obtain the schedule for servicing, and the number of entries per event would still tend to be large. Method (a) (ii) simplifies the editing by reducing the amount of data per event. This means that more storage space is required since time value information is repeated, and a little more processing could be required. Method (b) carries the splitting tendency of (a) (ii) a further stage. This simplifies even more the data entry methods but complicates the processing operation since a sorting is required to determine the next event. Also, the chance of errors occurring when modifications are made can be increased if the divisions tend to fragment storage of tasks which are allied. For example, if method (b) (i) is used, so that each task is given a different schedule, then the switching schedule could be altered but the related machine-start schedule alteration forgotten. Hence the replay would be started at the wrong time. Division into separate source schedules, method (b) (ii), has advantages since some tasks such as replay machine control and item identification are source orientated. However, the large number of sources compared to destinations makes this method unwieldy. In the small station which supplies only one destination, method (b) (iii) does not apply, and either type of method (a) could be used. In large network systems such as that of the - 140 - TIME - COMMENT 12:27:00 Identification of N1301 on Source no. 12 12:29:57 Fade Output Down Slowly 12:30:00 Start Machine no. 12 12:30:00 Switch Destination (Output) to Source no. 12 12:30:01 Fade Output Up Fast Figure 5-2 12:27:00/ID.S12.N1301; 12:27:00/ID.312.N1301; 12:29:57/F01; 12:29:57/F01; 12:30:00/ST.S12; 12:30:00/ST.S12/SW.S12; 12:30:00/SW.S12; 12:30:01/P10; 12:30:01/F10; (a) (b) TIME / SOURCE / FADE / IDBNT; 12:30:00 / TAPE / 01:10 / N1301; (c) Figure 5-3 LEGEND F00 Fade Up Slowly F01 = Fade Down Slowly F10 = Fade Up Fast F11 = Fade Down Fast ID = Identification no. S12 Source Unit no. SW = Switch Source to Output ST = Start / Task Delimiter • = Name Delimiter ; = Event Delimiter (Operational comments such as item title and duration could be placed after this symbol) 141 A.B.C., described in section 3.2.4, a separate schedule for each destination has advantages. Operations are directed towards supplying programme material to various destinations and even though standard groupings of destinations do occur, separate schedules allow errors to be noted quickly. In particular, each destination is fed from one source at a time only (except for the special effect of mixing, or superimposing two items) and must be fed continuously from some source, so the destination orientated storage allows errors of this nature in switching schedules to be readily detected. Separate destination schedules causes duplication of data which is source orientated, but these redundancies can be merged during the time that the next event is located. In choosing a method an important point is the number of scheduled tasks that will require service at the same time value. If there is only one task per instance of time, then the difference between (a) (i) and (a) (ii) disappears. As an example of different schedules, consider figures 5-2 and 5-3. Figure 5-2 shows the tasks and respective timings required to present for broadcasting item no. N1301 at 12.30 pm to a previously defined destination. As shown, two tasks are listed for service at 12:30:00 exactly, although in practice the execution of switching could be delayed by 0.5 seconds to centre it in the period of silence and also to allow a standard time signal to be broadcast at exactly zero seconds. (The final "pip”, which commences at zero seconds, last for at least 300 142 - milliseconds to enable volume level setting; the ’’pips" are broadcast on the hour in Eastern and Western states of Australia, and on the half-hour, at present, in South Australia and Northern Territory). In converting the events listed in figure 5-2 into a schedule, consider first the effects of using the systems of method (b). "Figure 5-2 contains four tasks, namely: item identification, fading, machine starting and switching. If division into separate tasks were used (method (b) (i), then the reference to identification would be stored in a different section to that of machine starting or of switching. This fragmentation can introduce errors if data entry works directly into these separate schedules. If the schedules are extracted from common input data then extra processing is required to carry out modifications to entries. If division into sources is employed (method (b) (ii)) then the fading task is difficult to classify, since it is not associated with a particular source (i.e., it is not source orientated). Since the number of sources is usually much greater than the number of destinations it is more economical to associate faders with destinations. Also, in multi-destination feeds, the fading requirements of some destinations could differ from others connected to the same source. Hence faders are better treated as destination orientated. Another problem of method (b) (ii) is that in large stations the number of sources is large so data entry into many schedules is awkward, although - 143 - if the control system performs the source allocation itself, size will have little effect on the data entry. The third classification, (b) (iii), classifies according to destinations, A.s figure 5-2 is written for one destination only, this aspect will be discussed later, Figure 5-3 (a) and (b) show the events of figure 5-2 transcribed into typical data input format, or language, using method (a). Figure 5-3 (a) shows each task listed as a separate event, which illustrates method (a) (ii); whereas figure 5-3 (b) illustrates method (a) (i). The one difference in this example, is that the two tasks, "Start machine no, 12" and "Switch Destination (Output) to Source no. 12", have been separated in figure 5-3 (a) and merged in (b). This saves a line of data entry, but means that each line must be scanned to extract all the tasks* In the case of a one-destination station, the number of time-coincident tasks is small, so method (a) (i) is satisfactory. Storage space is conserved since the time value is not repeated, and the increase in processing complexity is not great. For the case of a multi-destination station, however, the problem of specifying the relationships of tasks and sources to a particular destination arises. Method (a) (i) would give a marked increase in the amount of information required per event (i,e., per time value), with consequent difficulty of editing. Method (a) (ii) would become prolix if reference to each destination were treated as a separate event. Some space would 144 - be saved and editing made easier if a combination of methods (a) (i) and (b) (iii) were employed, since the storage advantages of (a) (i) in the single-destination case and the ease of data entry and editing in (b) (iii) would both be utilised. There would be some redundancy in the storage because of the inclusion of source orientated material, but the disadvantage of extra processing during servicing is overshadowed by the advantage of simple input communication. If more extensive "software'1 interpretation is used during processing of input data, more concise data entry formats can be obtained. This is illustrated in figure 5-3 (c), in which a single line is used to enter all the data indicated in figure 5-2. The format is fairly rigid, although the interpreter could be designed to ignore any "space" characters. To specify the source the word "TAPE" has been used, it being assumed in the example that the interpreter allocates a tape replay unit to the item known as N1301 (in fact, source no. 12 would be chosen). The fader specification is rigid also, the fade preceding the switching event being stated first, using a pre-assigned code. 5.3.3 Servicing the Schedule In order to correctly execute the instructions contained in the operations schedule, the computer requires two items of information: (a) the time at which the next operation is due to occur (called - 145 - the "next event time"), (b) the storage location of the data specifying the next operation (called the "next event address"). These two items are stored by the computer*s operations supervisory program (called ... (please turn to next page) 146 - COhJr/fl/UED FOLLOWING PA&i£ Gerr d&T. * 1 n^kt a/£vr Tiwe C{°LJ>") G£T OLST. #2. rv N£- nwe bi£xr D&r (b&u" r/Mu ) '\jtrvzy s' pcrzFM^d D£ST/fi/ArtOAi$ fo£v-Jyi/tm ' U£xr £l/£h/T Fit s-Fuut bj Fjmmi fji schedule m/cE -147- v V car of Com Pa Fa. TIVKS fof SHIFT OOMfUTLK Tttft W>7H N£XT'A/&JT SfeUTteo Di£$r. msK TtM£ ____ v fATWtN foF V S£*//c^- next ta<>ks D&r. V SET up NZ'TIfie A HO hDOdeSi FOX TV'S DCST V y« M <■- f^fASK //VO/£ATZ/>------: y T/M£S zqOAL- &ET M/kSk, TO STAFF TEiTlNO Z2"sr EAU) AV P£!>r. # / SCHEO ulA's Nc-T/Mf fc£ Sf>TEN\ N£'T/t*i V V CoMTirJufrioN orf PA&V/OUS PAf£ Fit. S-S(part gj FLOWCHART FOR SCHEDULE SERVICE 148 - the "operating system") and the next event time is compared to the computer’s internal clock, computer time. The comparison, which should be made each second because this is the precision of the schedule’s time data, is performed by testing whether the value of time, in hours, minutes and seconds, of computer time is greater than, equal to, or less than that of next event time. To initiate comparison the unit-second increment operation, triggered by the counting of the real time clock interrupts, is used as the condition for comparison to occur* If computer time is less than next event time no action is taken. If computer time equals next event time the computer executes the tasks to which the next event address is pointing. If computer time exceeds next event time then either the supervisory program contains errors, or a failure in computer or power supply has occurred at some time. In the latter case, when the condition is noticed, a search routine would locate the correct present event and execute it. After execution of tasks, the servicing routine sets up the new values of next event time and address. In the case where there is only one schedule (a single destination station) the servicing routine merely transfers the time and address of the next sequential event stored in the schedule. Where several schedules are used, the servicing routine must test each schedule to determine which event is chronologically the next. One method of performing this is to store the next event time and address for each schedule, and after task execution for an event 149 - SC HE DOLE FOIL: DES T'WA T /OfV #7 TIME TASKS ~7fT EVENTS V system DESTINATION *1 Time ME XT E VENT V£\r EVENT aod^e ss PG/NTEP TIME oest/natiom DESTJN AT/on 1 Z 3 4-5- MASK PEST/NATION EZ NEKT EVENT POINTED PEST//VA T/ON #3 destination *3 NEXT EVENT POf/vT£A TIP E4N1 $CH£MLL STORAGE 150 - is completed these pointers are re-set with the next sequential event for that schedule. The true next event time is then determined by testing each set of pointers, and a special set of memory bits (or memory "word") is used as a "mask” to indicate which schedules will require service at this next event time. When the next event time is reached, the computer goes in turn to each of the schedules requiring service and uses the next event address of each to determine what task is to be executed. A flow diagram of the method is given in figure 5-5 (overleaf). Figure 5-4 (a) indicates the use of memory in storing schedules for separate destinations. In order to move from one event to next earlier or next later event in the schedule, either the events must be stored contiguously in memory, or each event must contain information on the location of its previous and next events. This latter method enables time-sequential events to be stored at any location in memory, which has the advantage that editing processes in which events are added or deleted can merely change these address pointers, and extra data can be stored at some other location in memory. Figure 5-4 (b) shows a memory "map” of one event, containing two tasks. Following the task data are three address pointers. The first points to a remote area in memory which contains information which is not necessary for the computer’s operations, but is useful as comments for operators. These comments could include details such as item title or duration. The other two pointers indicate the initial location in 151 M£A1oAy LocATiorJ * toooo 7\ (OOO / 7"A5 K 1- OFEpKf{TlON (Oo oz tasa: f OfePAN i> /COG 3 TA^K 2. ' OPt/tAT/O/V £]/lENT i ooo 4 TA-JK Op£AAh/D / oo ojr u comments " POnJTE-P. IGCO& PFEViOU^ 6.\JENT pOf/V T£/Z i ooo 7 F/C. 5-4(b) MFMOPY MAP m ChiF\Ul 152 - memory of the previous and next events respectively. The initial location for the event listed in figure 5-4 (h) is labelled "*10000". 5.4 ITEM P lid S Eh T AT I ON METHODS 5.4.1 Assembly Methods A computer controlled system can be simply developed from the One-Man Operator scheme of section 3.5.2. The computer takes execution control of the replay machines, faders and signal distribution switcher and operates these by reference to its clock system and operational schedule. To perform this the computer needs control and data path connections with the replay machines to start items and to retrieve information concerning identification. Major items (those with sufficiently long duration to be indefinite) are treated either as live remote broadcasts, similar to outside broadcasts, or are pre-recorded and reproduced on reel-to-reel machines. The computer requires a cueing signal from pre-recorded major items to indicate that the item is finishing. A live item will be expected to time its duration correctly to its desired value, although some cueing facilities would be useful for outside broadcasts, which have to cope with independent time-tables and the vicissitudes of weather conditions. The announcements and fill-ins are recorded on cartridges or cassettes and these are placed in multi-cartridge replay units so the computer can rapidly select a number of announcements in 153 - any sequence. Centralisation of replay equipment can give savings in both equipment and staff numbers, in multi-destination stations. Instead of keeping spare equipment in each continuity suite centralisation allows the spare units to be shared, enabling a reduction in the total number of replay units. Centralisation does introduce a problem of monitoring of technical quality, since it is difficult to concentrate attention on more than one sound simultaneously, and also the assembly is not completed until the switching stage. The staff engaged in loading replay units would no longer have to be skilled in monitoring technical quality, so they could have a lower standard of training. The demand for item loading is not continuous and, although several items could commence at almost the same time, loading of machines can be staggered since it can be performed some time in advance. Hence the replay operations staff could be almost continually busy in loading, unloading and rewinding recorded items. The allocation of tape replay units for item reproduction could be performed by the computer, with the aim of achieving maximum utilisation of equipment available. In the event of failure of a machine, the computer can quickly modify its allocation of machines to surmount any problems. The difficulties of cueing and controlling disc recordings make its use not worthwhile in an automated system. Automated reproduction of disc recordings is used extensively in consumer- market record players and in "juke-boxes”, but the requirements 154 - DtSfUthTiOh/S / 2 5 4 5" 6 78 S~ tO } D - 8 TOTAL Of ULOtt-Po//v7$ - %0 HQ. 5~G MATRIX WIT CM 155 - of cueing and identification are not necessary for these applications. In broadcasting, accurate identification of the item, which could be one of a number of items recorded on the same entity of storage (for example a tape or disc), and precise cueing of the start are essential, and to develop these for discs requires special signals to be recordable on the disc and, as well, intricate mechanics to control the turntable and arm carrying the stylus. The proscription of disc replays means that items at present stored on disc (as most commercial recordings are) must be transcribed onto tape. This adds appreciably to the initial costs and time taken to develop the automated system. However, it appears that commercial recordings will in future be available on both disc and tape media. 5.4.2 Switching Switching is necessary to connect the source of an item to one or more destinations. The switches could be mechanical (for example, key or rotary switches, or push buttons), electro-mechanical (relay or uniselector) or electronic circuits. The switch can be considered as a binary decision unit (either "ON" or "OFF") even if the physical operation is sequential, or stepping (as in the rotary switch and uniselector). A system of switches necessary to connect a collection of S sources to I) destinations can be considered as a two dimensional array, called a matrix switcher. Figure 5-6 shows a matrix of ten sources (S = 10) and eight destinations (D = 8). -156 - PEST/NATiOfifS 1 Z 3 4 s' 6 7 8 AA/KAA/K/K/N COUCZHTkf\TOk'-> J> ■- 2 /Vo. Of SOOtLCH C/OSS'Al/A/n /Vo. OF CAoV-fO/AFTi ~ 24 TOTAL OF CA.CX' pO/rSTS FIT 5-7 DflfCrATlOF WITCHER 157 - Each "x" on the diagram represents a binary switch, each switch often being called a "cross-point”. The characteristic of broadcasting of many sources to a single destination implies that one, and one only, cross-point should be closed per vertical column of the matrix. This simplifies the control of the matrix switcher, because a single identifying signal can be sent to each column to close one of the cross-points. The cross- points making up a column should be linked in such a way that, should one cross-point be closed by the computer, the others are opened (in the case of sequential devices, such as uniselectors this is built-in). The identifying signal could be a binary or BCD number which is decoded at the switcher by logic circu.itry. The matrix switcher of figure 5-6 allows all combinations of sources and destinations, but requires eighty (10x8) cross-points. In cases where the destinations never have completely independent programmes an alternative method, known as a delegation switcher, can be used. This arrangement, shown in figure 5-7, uses a bottleneck, or concentration, to reduce the number of cross-points needed. Two stages of switching called source switching and destination switching are linked by three (C = 5) concentrators. In the arrangement shown the source switcher contains thirty (10x3) cross-points and the destination switcher twenty four (8x3). The number of concentrator links restricts the number of independent programmes of broadcasting material that can be transmitted simultaneously, but this kind of situation is quite common in network broadcasting. 158 - Delegation switching is economical only if there is a fairly severe concentration of sources. Considering S sources, D destinations and C concentrators, the conditions are: Size of matrix switcher = S.D ...(5.1) Size of delegation system switchers = S.C + C.D ...(5.2) = C.(S + D) ...(5.5) The condition for an economical delegation system is: • • • • 4^ C.(S + D) S.D VJI / S.D G <----- ...(5.5) S + D 2 + £ < 1 ...(5.6) D S \ Now S, D and C must all be positive integers, and C ^ 2 for any useful destination switching (i.e., if C = 1 then no destination switcher is required). From equation (5.6) it can be seen that C must be less than S or D for saving in the number of cross-points to occur. i.e., C S, D ...(5.7) Since it is usual for S D ...(5.8) equation (5.5) can be written as: C < 1 + D ^ D ...(5.9) For the possibly more realistic case of: S » D ...(5.10) 159 - a useful criterion for delegation systems to be economical is: / D c <" ---- ...(5.11) 1 + 1 C | ...(5.12) In the example shown in figure 5-7, C was chosen to be 3, when D equalled 8. Hence: C (=3) < \ =4 The total number of cross-points needed for the delegation system is: 30 + 24 = 54, whereas the matrix switcher shown in figure 5-6 required 80. 5.4.3 Fading Fading is used to soften the transitory effect of switching from one item to another. It can be used both as a presentation tool and to suppress unwanted clicks or transients produced by the switching process. In presentation it is used to slowly change the volume of the sound so that item changes are smooth. Operational fading can be of two types: a complete fade to silence before the next item is established, or a cross-fade in which both signals are superimposed temporarily as the concluding item is faded down and the new item is faded up. The latter is sometimes called a "mix" or a "dissolve". The fade through silence is often used in a multi destination system when some destinations must leave or join a 160 - DtSr/UAT/ONS 1 2 3 4-5-6 7 S MS Tlm TIOM FADEFS EFFECTS, FA PEAS 1 £ 3 4- S' G 7 8 9 10 S cokces Total eumfea of uo^-Ao//vrs, -Eofz^i. — 84- FIG-. 5~- 8 OELjOIlOl WITCHER WUMMl 161 source which is continuing to feed other destinations. To perform this operation there must be a fader associated with each destination, after the switching process. Also, to suppress switching transients the faders must be placed after the switcher. However, to perform cross-fading, the faders must be placed before the destination switching process. Since the number of destinations is small, it is reasonable to place faders in the destination feeds, but the large number of sources makes it costly to provide a fader for each source. Compromise arrangements can be used to incorporate cross fading effects into both the delegation and matrix type switchers. Figure 5-8 shows the arrangement for the delegation switcher. Here the number of cross-points in the source switcher has been doubled to allow each concentrator feed to be a selection of the output of two faders. The disadvantage of this increase is offset to some extent since the "half” of the source switcher which is not actually supplying destinations can be switched at leisure, so source switching becomes a pre-selection for the two faders supplying each concentrator. Figure 5-9 shows the arrangement which can be used with a matrix switcher. The method, known as re-entrancy, uses extra destination columns (also called output buses) as inputs to the effects faders, and the paralleled output of each pair of faders becomes another source (input bus) of the switcher. Thus, when cross-fading of two sources is required, the sources 162 - DtST/Z/AT/O a/S y Z 3 4- S 6 7 6 (Of\J /AT HE'ENfflMT a FAbEAS DEST/ r£7?^ NUM&F/l OF UO = /3£ EIL. 5-9 mm. SWirCHFR WITH FJM1 - 163 - must be switched to a pair of faders, with the present item faded up, and then the destinations which require the cross fade are switched to the fader output’s source-input feed. At the appropriate time the cross-fade is performed and the new source feeds the destinations, which are still attached to the fader output. Finally, the destinations can be switched back to the direct input feed of the new source. The calculations included in figures 5-8 and 5-9 indicate that the number of cross-points is increased to include faders in both switcher systems. However, the increase is only 40%o for the delegation system, but is 70% for the matrix switcher. The delegation system has the advantages that the source switcher becomes a non time-critical pre-selector, and that other signals, such as standard time signals or identification can conveniently be added at the concentration point. The re-entrancy method does have the advantage that it can be used to by-pass a faulty cross-point switch. This will be discussed in greater detail later. Both figures 5-8 and 5-9 show the positioning of destination faders on the individual output feeds of the switcher. In manual systems the speed of fading, controlled by the operator, varies depending upon the artistic interpretation of the fading act by the operator. In an automated system the fading speed must be defined beforehand. The fading speed could be selected from a set of preset speeds, the selection being defined in the operations schedule. Alternatively, the degree -164 — of attenuation could be controlled directly by the computer, by means of a time-generated sequence of numbers. This is converted to a control voltage using a digital-to-analogue converter. The preset-speeds method requires less programming and less hardware than direct control, and the perception of differences in fading rates is not acute, so the use of a number of preset speeds is more suitable for broadcasting. In fact, it is probably satisfactory to have only two fading speeds available, fast and slow. A suitable fast fade would have a duration of about half a second, or less, and for the slow fade about three seconds would be satisfactory. 5.4.4 Item Identification One of the major tasks of a broadcasting system is to ensure that items about to be broadcast are correctly selected, as nominated by the published programme of the station. This requires some process of identification of each item. A significant proportion of errors in manually operated stations is made up of wrong items being presented. Most items are given a name or title, but this often not unique. The item could form one element of a group, for example, " ’The Bandstand Show' number 4”; or it could be one of an ordered sequence, for example, " ’Our Mutual Friend’, part 4 of 10 parts”. In addition, the item itself could be segmented, and recorded on different reels of tape Thus, to - 165 - complete an identification process several separate -units of information must be combined. Many of the identification errors are caused by incomplete checking when part of the information is found to be correct. The use of a single code or number system would surmount this problem, but would introduce the administrative task of assigning and recording each identification code. Also manual identification errors are likely if the code is long or unwieldy. The identification process can be divided into two categories: (a) those items which are accessable for the purpose of identification testing for some period before the start of transmission, (b) those which are not accessable. Items of type (b) are usually not accessable because part of the source equipment, for example the transmission lines, are in use for other transmissions up to the commencement time of the item. In these cases identification must be made as soon as the broadcast commences. In manual operations this is done by having the continuity staff listen carefully to the opening sequence of the item to positively identify it. If the wrong item is presented the staff discontinue the relay and substitute fill-in material until the correct feed is established. In an automated broadcasting system employing a digital computer, the use of digital codes suggests itself, with the 166 - code generated or reproduced at the source and transmitted to the computer for comparison with the identification code listed in the operations schedule. The tasks required to implement the system are: (a) the allocation and maintenance of a register of identification numbers, (b) for pre-recorded items, the recording of the identification number on the head of the tape, (c) the inclusion of the identification numbers in the operations schedule, (d) generating or regenerating the code for testing at pre-broadcasting time, (e) identification checking by the computer, (f) error and default action by operators. The allocation and filing of details of identification could either be performed manually or by a controlling program within the computer. Obviously some system is necessary to avoid multi-labelling with the same identification number. With the case of often repeated topical items, such as "National News", a common identification number would suffice. The item's identification code must be generated a short time before the broadcast commences, so that errors in item selection can be corrected. V/ith live items the code would be sent by the staff preparing the item. With pre-recorded tapes it is desirable that the identification number be - 167 - recorded as a prelude to the item on the first few feet (the head) of the tape. This recording would become part of the line-up routine preparatory to the recording of the item. It is possible that this task also would be performed by the computer, eliminating the manual-encoding error possibly introduced by the recording operator. A difficulty arises with the use of "foreign" pre recorded items which are "imported" from external organisations. These tapes could either be handled manually, or could have a special "leader" of tape spliced onto the front of the foreign tape. A suitable identification code and other line-up signals could then be added. An identification code would be included with each entry in the operations schedule, and at the time of item identification is compared with the code recovered from the item's presentation source. For pre-recorded items this recovery would be accomplished by the computer's initiation of replay of the leader which contains the identification. For live, remotely produced and non- accessable items the code is intercepted from the programme signal-carrying line. For the first two, the code is transmitted at a random time on the unused line and for the last, transmitted a specific interval (say 1 second) after the item was due to commence. If the identification comparison fails, the computer would initiate remedial action. If the item is a non- 168 - accessible one already switched "on-air” the feed would be disconnected and silence substituted. A message would request operator action either to substitute fill-in music (if a non-accessible or remote item) or to load the correct item (if a local item). To overcome the case that the identification code or testing process itself is faulty, the operational staff must be able to override the test result, and direct the computer to continue with normal operations. 5.4.5 Item Commencement Cueing If all item durations and commencement times are known accurately, cueing for next-item commencement can be taken from synchronised clocks. However, since this is not so, the need arises for the issue of a cueing signal by the indefinite-operation item. Particular cases of indefinite- operations are: (a) the conclusion of a long duration tape replay, (b) items whose commencement, conclusion or interruption depend on external factors. An example of (b) is the sporting outside broadcast. It would be desirable for operations staff at the remote broadcasting location to signal their readiness to commence or conclude the item. To transmit cues either the programme-signal lines or separate cueing-only lines could be used. The choice is a matter of relative cost, that of the extra line compared to 169 - the cost of intercepting non-audible signals on programme lines. For local sources, studios and tape replay units, the separate line is probably cheaper, but for remote broadcasts the cost could be comparable. Similarly, cueing signals coiild be recorded on tapes on the programme-signal track or on a separate track. An alternative is to place a temporary mark on tape, such as a strip of light reflecting material. When the tape is to be erased and re-used this can be removed. However the reliability of this method is not as high as that of the signal-recording method. Two problems that occur are the need for advanced warning and the introduction of "foreign" produced tapes. Some sources, in particular some television video tape replay units, take a few seconds of time to reach the correct speed and phasing and so require a cueing signal in advance of the event about to occur. This "dead time" must be taken into consideration when designing a cueing system, and appropriate delays built into an automated cueing and switching system. The foreign tapes must be cue-marked in a similar fashion to internally recorded tapes. For this, a temporary marking system is most attractive. Alternatively, the item has to be copied ("dubbed") onto another tape with the cues inserted. 170 - 5.4.6 Time Announcements An important service rendered by broadcasting stations is the accurate announcement of the time-of-day. Indeed, together with the broadcasting of the official time signal (the ’’pips'*) provided by the post office, it is probably the most popular method of synchronising personal time-pieces. (Other methods are: comparison with the P.M.G.’s "speaking clock", PMG radio station TOG, or clocks on public buildings e.g. "Railway time".) In an automated broadcasting system consideration must be given to the recording of time announcements for subsequent replay as a part of the station*s presentation* Time announcements can be recorded only if their reproduction can be synchronised to the clock system. Hence the announcement could not be recorded as part of a long tape replay, unless the replay were precisely time-controlled. Otherwise, short tapes must be used, or tapes with only short segments replayed at any one time. The characteristics of time announcements in a broadcasting system are: (a) accuracy to nearest 7 minute, (b) randomly commenced within the minute, (c) blended into the station*s presentation so as not to cause uncomfortable disruption to listening. These characteristics differ from those of the PMG speaking clock, which provides time calls at fixed intervals of 10 171 seconds and accompanied by a time signal. To provide suitable time announcements the system must be available immediately on request, possibly to several separately assembled programmes within the minute period. The ease of changing the announcers voice to suit the main presentation must also be considered. Three methods of recording suggest themselves. These are: (a) sequentially recording on magnetic tape, (b) part-sequential and part-random on rotating devices such as disc or drum, (c) effectively random-accessed digital storage such as core or MOS memory. 5.4.6.1 Magnetic Tape hetliod Since access to material on the tape is sequential, time must be allowed to reposition the tape to the start of the next announcement, if the previous one was not used. This period of time can be found by distributing the following time announcements between several tapes until sufficient idle time occurs between adjacent announcements on the same tape. In practice, an announcement such as: "THIS IS STATION XYZ ___ THE TIME IS TEN PAST TWO" would take less than 5 seconds, so with new announcements each 15 seconds only one idle period is needed for repositioning. Thus only two tapes, with announcements accessed alternately, are required. Figure 5-10 shows the arrangement of 172 - TIME (Mutt)------> - lA o t'u + '/z. + 3/4. f / I______j______!______!______!______L TftPt 1 (WITH ODP - minutes) TAPE 2. (w/TH £(/£N *4-'M/Morns) A NN OUNCE MEN T Pt-K/CE> /7& S-10 DISTRIBUTION OF TIME /H/mMMENTS TIME (M/Ni) ------> ~ ^4 O E ^4 i E t ___ I______!______I______!______|______L __ ^ __ —u TAPE 1 4 TAPE Z 1 1 PTE Sc NT TIME'CALL AlAd y LETtE/VD*. ^ TAPE ApVAHC/f/E I------1 A/£*r 7, ME-CALL HEADY ■* Then pK£pL/\Y//* FICS-II AMTCEMEU T OF RECDRDITM - 173 - recordings on each of the two tapes, compared to the passage of time. Using computer control, the advancement of each tape is simple. If a request for a time announcement is found in the schedule, the computer selects the tape unit with the appropriate announcement, starts the replay and switches it to the desired destination/s)• At the end of the announcement the tape is stopped, either by the computer counting a specific time interval, or by a cue recorded on the tape. If the announcement on a tape is not requested by the end of the appropriate -j- minute, the computer replays that announcement anyway, to re-cue to the next announcement, but does not switch it non-air"• Figure 5-11 shows the method and time scale involved in controlling tape advancement. Disadvantages of the tape method are lack of multi-access and cost of providing different voices. A separate dual-tape unit would have to be provided for each programme presentation wishing to access a time announcement within the same minute period. The difficulty of providing several voices is one of preparation time and cost. If the recordings are made at a tape speed of 1 7/8 inches/second (which would give sufficiently good quality for time announcements) and each announcement runs for five seconds, then about ten inches of tape is required to record one time announcement. Now, for each tape there would be two announcements to cover one minute of time (i.e., four announcements of i~ minute intervals distributed between two tapes), so for calls covering a - 174 TA Ft / . TKACK / ------> RoPLA/ P i RETCT/OH ------2^-1------:------5 HOUR 5 3 HOOKS 3 HOOKS 3 HOURS 3 KooKS 3 HOOKS 0 M/A/S Fz, M/aJ / M/a/ /A. M/HS 2. M/a/5 2-PE M/hJJ 10 HOOKS 10 HOOKS TO Hours /o HOURS TO KOOKS To HOURS v5~9 'Al. M/Hi S"9 M//Ji EGEu M/k/S S' & M//ZS EyA, m/aj s ST y M/a/5 PE Pi Ay Pi Root /oh <------TRack Z TAPS 2- TTACh / ------> RKHray P/Rotct/oh 3 hours 3 /hours 3 HOURS 3 Hours 3 HOURS 3 Hours [/4- M/H M / rJ PA- M//vS / 5/4 tf //j 5 yJ4 m/// j y ^ m//vs TO HOURS /p hours TO HOURS hours TO Hours EQ M/a/5 E9 rt/A/S EG %/ m/a/s EBP/ M//J S E7 Pb m/a/S sy'/ FIG. 5-11 fa) TM rjm TIME RFCCRPm tape 1 ^ track 3 HOOKS To syouRs 3 hours TO HOURS 3 hours TO R&uRS 0 M//VJ EQTi M/a/s Pz. m/a/ E9 m/a/5 / M /H . EQ/R m/aJS I > <— ------> <------> 4 AePLA y P/Atrcr/oK TAP* Z track -Gr r 3 HCuR5 TO //tUR\ 3 //curs TO HtuKS 3 /tours Tc? /RCuRS '/ 4- 4- > 4- hero a y p/a *cr/ ok FIE S- 1Z [k 1 WELL IRAK UK miMFi 175 - twelve hovir period, of true time, the number of calls would be: 2 X 60 X 12 = 1440 Thus the length of each tape would have to be: 2 X 60 X 12 X 10/12 feet = 1200 feet However, the problem then arises as to what happens when the end of the tape is reached, after twelve hours. If the calls are simply sequential each tape would have to be rewound, and time announcements would not be available for broadcasting during this time. To avoid this the dual-tape replay system could be duplicated, but this would be wasteful unless the second unit was required for another independent programme. It v/ould be necessary to stagger the initial time announcement call of the different sets of tapes, so that both units would not require rewinding at the same time. Also, the multi-access advantage v/ould be limited during the period of rewinding. A preferable method is to use a tape transport system which can replay in either direction. Either a tv/o track or one track recording system could be used. Figure 5-12 (a) shows the tv/o track system, with the first six hours of announcements recorded alternately on the top tracks of the two tapes, and the second six alternately on the bottom tracks. After six hours of replay the direction of replay is reversed, cued either from the computer or an Mend-of-recordM signal, and the output of the other track*s head is taken. Using a single track system, the forward and reverse-direction announcements are alternated on the track, as shown in figure 176 - 5-12 (b). The tape advancement is a little more complicated, as one time announcement call must always be advanced, and if the contemporary one is not used then two announcement sections (this one and the following reverse-direction one) must be moved past the replay head. Thus the duration of each announcement must be no more than \ of the interval of time covered by the announcement. The advance could be controlled easily either by a local cue-signal method or by the computer. However, some care should be talien to ensure that the reverse- direction announcement is not moved past the head whilst the replay is still ”on-air". Regarding the tape itself, the figure of 1200 feet per reel would have to be doubled for the single track system at the same recording speed. A 2400 feet reel of tape is usable, but the low recording speed of 1 7/8 inches/second is marginal for voice quality. Another problem is that of wear in tapes which are in constant use. If several voices are used, the wear is distributed over several tapes, so the problem is not as severe as that with the Post Office Speaking Clock. Alternative methods which surmount any wear problems are discussed in the next two sections. To enable tapes to be changed, either because of wear or to change the voice, a spare dual-replay unit would be used. This unit would be required anyway, to protect against a failure of the operating system and would normally have a copy of the announcement tapes, stepped in the same manner as the operative unit. 177 5.4.6.2 Rotating Memory Methods The methods of recording on a disc or cylindrical surface avoid some of the re-positioning problems of magnetic tape recordings. The Australian and British Post Offices use these methods to generate the ’’speaking clock" time announc ement s• The Australian Post Office at present employs a set of glass discs which rotate at 30 r.p.m., driven from a stable 100 K Hz source. The method of recording on the discs is optical, and this has the advantage of eliminating wear, since there is no mechanical contact between the disc and the replay 2 transducer. The quality is fair, the main limitation being the relatively poor signal/noise ratio of 30 dB. There are three discs, one for the "minutes" call, the second for the preamble, or "phrase" and the "hour’s" call and the third for the "seconds" call and the timing "pips". ^ The "phrase" (’at the third stroke’) and the "pips" are each recorded on a single circular track, and so do not need any head re-positioning. The other components of the time announcement, for example: ’it will be one’, 'it will be two’, etc., are recorded on separate tracks which are accessed by movable heads. To avoid an interruption whilst each movable head is being returned from the disc centre to the outside track, the recording sequence is interleaved in a similar manner to that described in the previous section. The British post office has introduced a magnetic drum 178 - recording system, which consists of a neoprene surface stretched over a brass cylinder. The neoprene is impregnated with magnetic iron oxide and has the time 5 announcements recorded on circular tracks around its periphery. The system of fixed and movable heads used is fundamentally similar to the Australian Post Office*s optical system, except that only the ’'minutes" and "hours" heads move. This is the most economical compromise between the single moving head and the fixed heads with switching methods. The magnetic recording gives a higher quality than the optical, but has the disadvantage that parts wear out more quickly. Head-to- neoprene surface wear is minimised by using a film of silicone oil. To adapt these devices to the broadcasting operation immediate access to the start of the announcement is required. This could be obtained either by freezing the rotation until a request is received, or by employing several different complete sets of replay heads. The first method is practical but might be prone to mechanical failure and have appreciable delay before reaching correct speed. The second method would be expensive, since for a two second rotational period (30 r.p.m.) at least four sets of heads would be needed. However, it has the added advantage of enabling multi-access to the announcement. In both methods it would be necessary to know the location of the announcement starting point. This could be done simply by using a lamp (or light emitting 179 - diode) and a photo-electric cell, either directly with one on the shaft, or fixed with a half-silvered, half-dark disc positioned on the shaft. A more difficult matter is the need for interchangeable recordings. In the Post Offices the installations are fixed and this results in a highly reliable service. Neither the optical disc nor the multi-head drum methods lend themselves to frequent changes in the recording. The first problem is that the discs, fixed head arrangements and mechanical drives are fairly fragile and secondly it would be expensive to record and store several copies or recordings. One point at which the Post Office clocks exceed the needs of broadcasting is the precise synchronisation to an external time reference. This is typically within five milliseconds of reference time.^ An accuracy of one or two seconds would be sufficient for broadcasting purposes. To summarise, the utility of rotating drum or disc systems depends on the broadcaster’s desire to be able to change voices. If this is not required then these systems are practical, with the magnetic drum being preferable because of higher reproduced quality. If frequent voice changes are required, a reduction in reliability would probably result, because of the difficulty in swapping recordings. Hence these methods would not be recommended. 130 4.6,3 Digital Random Access liethod The characteristics of time announcements in broadcasting suggest that digital recording of time calls is feasible. The number of words spoken in any call and the repertoire of words are small, so a synthesis of the call from individual words or even syllables is worth considering. The advantages of such a digital system of time announcements are: (a) multi-access, (b) easy recording session for a particular announcer*s voice, (c) different voices stored on magnetic tape, either in analogue or digital form, (d) no re-initialisation (e.g., rewinding) or announcement v. time synchronisation (e.g., clock and tape out-of step) problems. Two difficulties that could be experienced are: (a) a fairly large store (say >2 million bits) would be required, (b) the transferring of data in real time from the analogue signals to digital storage. A typical time call would contain up to twenty syllables and, at a rate of four syllables/second, would take five seconds to speak. One of the longest calls would be: / iii ii / // iiii i " This is the third network (pause) the time is seventeen / / / till minutes past eleven IT ...(5.13) 181 ( ! ‘ represents a syllable, lasting second). In this particular call the number of different words is ten (excluding the pause). The time call repertoire would consist of: (a) the cardinal numbers : "one" to "twenty" inclusive; (b) time identifiers : "minutes", "o'clock", "quarter", "half", "quarters"; (c) the connectors : "past", "to", "a", "and", ...(5.14) This gives a total of twenty nine words, or forty five syllables. a saving could be made by working in syllables to remove redundancies. This would require: (a) the syllables : "thir-", "fif-", "-teen"; (b) cardinal numbers : "one" to "twelve" inclusive, and "twenty"; (c) the identifiers listed in (5.14b); (d) the connectors listed in (5.14c). ...(5.15) Removing redundant syllables reduces the number to thirty three syllables. However, there could be difficulties in matching the speaker's intonation of adjoining syllables, so the full-word synthesis method is to be preferred. To convert the speech analogue signal into digital form pulse code modulation (PCM) could be used. .Alternatively 7 delta modulation could be used but its main advantage of no-requirement for word synchronisation is lost because of the word-orientated storage met od of digital computers. Selection of sampling rate and number of quantising levels is important 182 so that the audible characteristics of bandwidth and signal/ noise match those of other signals within the broadcasting system. Since high level speech characterises time calls, the bandwidth and signal/noise (i.e., dynamic range) need not be great. 8 H Hz bandwidth and 50 dB should be sufficient to reproduce speech that is not obviously degraded compared to other announcements. Since the sampling rate must be at least twice the bandwidth, a selection of 20 K Hz sampling rate is suggested. To choose the number of quantising levels o consider the formula given by G-reefkes and Riemens for PCM: (in dB) (S/N) max if +2 ...(5.16) n 8 . n where n = number of bits per code group i.e., n = \ (S/N - 2) ...(5.17) n - 48 for 50 dB, S/N = n “ 6 =8 ...(5.18) Hence a quantising system of 8 bits (256 levels) could be used. Signal/noise can be improved by companding,J which in this particular use would probably be cheaper than increasing the number of bits/word since the storage required for the time calls would rise. The total storage requirement can now be calculated. The time-value announcement itself requires 45 syllables to be 182 - stored. In addition, there is the pre-amble: "This is *****, the time is..." which could require up to nine more syllables, viz., "this", "is", "the", "time", and the five * * s ...(5.19) Hence the maximum number of syllables could be 54* With : 54 syllables, 4 syllables/second, 8 bits/sample, 2 X 10Zr samples/second, the number of bits required is: ^4 X 8 X 2 X 104 = 216 X 104 bits = 2.16 M bits ...(5.20) The present cost of core memory is about five cents/bit so a core store of this size would cost over $100,000 (ignoring quantity discounts l). However, rotating disc storage costing $10,000 - $15,000 has storage of about 4 M bits for a platter. Disc systems are produced with a fixed-head recording system, which is more reliable or with removable disc platters (moving heads). The latter system would aliow each announcers voice to be stored on a separate platter; however removable disc systems are more expensive and more prone to failure. Assuming that the digital code is stored on a disc, to reproduce the analogue signal the code must be fed to a digital-to-analogue (D/A) converter at the correct sampling rate This introduces the problem of matching the data transfer rate 184 - from the disc to that of conversion, A solution is to use a static memory such as core, as a buffer. 16 K of 8-bit unit core memory would allow 800 milliseconds, or three syllables such as "eleven" or "seventeen", to be stored as a unit. The disc transfer rate using direct memory access is about 100 K 8-bit samples/second (about five times the conversion rate) which is sufficient for this task. The maximum disc latency (the maximum possible time delay before the data arrives at the pick-up head) is commonly 40 milli seconds but this is acceptable as part of a pause between words. As an alternative to a large buffer a smaller "wrap around", or circulating buffer could be used, although the addressing problem for data transfers would be greater. In transferring the analogue speech to code on the disc a computer controlled recording and editing session is recommended. The announcer would record on a conventional analogue tape recorder different selections of time announcements arranged to give several samples of each word in the time call repertoire. An editor-operator would then audition the recording to decide which words were to be placed on the disc, and would mark the start and finish of these on a cueing track on the tape. The computer could then replay the tape and switch each selected word to an analogue-to-digital (A/D) converter storing the resultant code at the desired disc location. Playback facilities would allow the operator to alter the cueing to obtain the desired delivery. - 185 - An automatic method of varying cue positions might be needed because of the time scales involved. Alternatively physical marking of cues on the tape is possible if high recording speeds are used (say 15 inches/second). Aith this recording method inter-word pauses are recorded as part of the words, with disc latency providing an uncertainty of - 20 milliseconds, which is acceptable. In assessing the worth of this method of recording time announcements three points could be considered: cost of development, quality of reproduction and simplicity and ease of operation. Typical hardware costs are as follows: D/a converter, with multiplexing --- <£1,500 A/D converter, with multiplexing --- $2,500 4 Million bit magnetic disc --- $15,000 151 K bit buffer memory core $6,000 Total $25.000 actually, these units could to some extent be shared with other tasks so the specific time announcement system cost would then be lower. Development costs v/ould aJ_so include software, to control time call synthesis and to control recording and editing, and interfacing the tape recorder control to the computer. Quality of performance can only be proven by field trials; however the use of PCM in the broadcasting field is now accepted for quality (e.g., the use in television of sound on syncs). The method does allow fairly simple means of changing 186 - the announcing voice. Once each analogue tape recording is correctly cued for word transfer it could be kept, and whenever a change in voice is desired, conversion and disc storage can be performed. Whilst more than one programme can access the announcement during the broadcasting of time to another programme, only one voice is available without re-conversion and storage. If satisfactory performance can be obtained, the digital storage system could be attractive to large, multi-network stations, where multi-access and changes in voice are desirable. For the single-programme station a magnetic drum system would be preferable, or if the cost is too high, magnetic tape units, which might cost about $5,000. One of the major advantages of the digital system is that the computer itself selects each time call word, so the wrong time will not be given provided the operational clock system is correct. This is not true of the first two methods considered which depend to a greater (magnetic tape) or lesser extent (rotating method) on position of the recorded medium for correct announcement• 5.5 THE COMPUTER AND TEAIPHlAUh3 The computer most suitable for use in the automation of presentation operations is the small, process control type digital computer which has now become commonplace in science and engineering establishments. Although relatively cheap 187 - smaller computers were available around 1960, it is only recently that advances in the area of peripheral units such as data entry systems, have enabled "conversational” means of exchanging data between the operators and the control system. This section describes the types and prices of currently available units suitable for broadcasting control, 5.5.1 Central Processor and .emory Units The development of C,P.U.* s has reached the stage where the size is less than 1/3 cubic foot. The present trend is towards the use of microprogramming as a means of decoding instructions, the micro-instructions being stored in Read-Only- Memory (ROM). This will simplify the maintenance of 0.1,11*s, which at present calls for considerable analytical ability. The computer is usually marketed in terms of a minimum configuration which typically includes: (a) central processor unit, (b) 4096 (4K) words of core memory, (c) teleprinter/key data Input/Ou ,put (I/O) device and its interface. This price for the basic set-up would be approximately S3,000 - 815,000, depending upon memory word size and computation speed. Accessory units consist of: (a) extra core memory up to about 32 K words 83,000/4 K (b) subsidiary memory : (i) disc - 16 K to 262 K words or more 88,000 to 815,000 188 - (ii) magnetic tape 810,000 (lit) rnagne tic d rum (c) fast paper tape reader and punch 84,000 (d) IBM - type - card reader 15,000 (e) power fail-protection of volatile C.f.U. data storage 1200 (f) real time clock 1300 A configuration suitable for use in computer-controlled broadcasting networks would contain a C.P.U., plus 16 K words of memory, power fail protection, and a real time clock. Subsidiary memory would be needed to store the operations schedule, and of the possibilities listed in (b), (c) and (d) above, disc is preferable because of its rapid access capability. Card readers are more suitable for batch processing rather than real time, although paper tape 1/0 is useful for storage of standard maintenance programs and specific programs developed for broadcasting operations control. Magnetic tape is useful for back-up memory of both core and disc, in cases where these are "wiped”; however its inclusion is not obligatory- Technical characteristics required for broadcasting control are good character handling and storage, and fairly fast speed, -Since alphanumeric character codes consist of eight bits, a machine whose architecture has a v/ord length which is a multiple of eight bits is veiy desirable in a case like broadcasting where c laracter 1/0 is important. 189 - Quantitatively, 16 bits/word is the optimum since smaller size has too restricted an instruction set, whereas larger size becomes too expensive. The time scales of broadcasting control do not require ultra-fast processing speeds; however, execution speed (which includes memory access speed) is a fundamental limitation on the number of tasks which can be performed in a multi-programming or time sharing operation. Hence high speed is useful since broadcasting control could in later development include many tasks. Instruction fetch/ execution time should be better than 2 to 3 microseconds. 5.5*2 Character Input/Output devices The standard typewriter and page printing device available for character entry and printing is the teleprinter/ keyboard unit. It is noisy and slow (ten characters/second) but is rugged and relatively cheap (around $1,500). With suitable sending equipment, called modems, the unit can be operated at points remote to the computer, communicating via telephone lines. For situations where the volume of data to be entered is small and fast printing is not required then teleprinters are satisfactory. If large volumes of printing or high printing speed are required, then the line printer is useful, as typical speeds are 300 to 1000 lines/minute. The line printer has several unfortunate features; namely, it is not so rugged, so maintenance costs are high, its purchase price is high, $10,000 190 - >20,000, and it tends to generate large amounts of paper. The main uses of a line printer in broadcasting would be in computer program development for the control system and printing copies of operations schedules, for situations where human operators require up-to-date versions and some other form of display is not available. Paster and better methods of presenting data to and from the computer have been developed in recent years for information retrieval systems, such as banking and airline bookings. Foremost amongst these is the display terminal which utilises a television picture monitor raster to display up to 2000 alphabetic and numeric characters using a matrix of 35 (5x7) dots. A silent keyboard entry unit can be switched to simply display on the screen, or transmit directly to a computer. Alphanumeric displays are of two kinds: the simple conversational, and the storage and editing. The former acts as a "soft-copy” teleprinter/keyboard unit, and is useful for conversational interaction between operator and control system. Its fast writing speed (up to 1200 characters/ second) enables "pages" of information to be displayed quickly, without wasting paper. The price ranges from about 32,000 to 33,000. The second type utilises the character storing memory in the display unit for modification and later transmission back to the computer of all or part of the "page" stored. It is particularly useful for "off-line" editing of data since "on-line" 191 conversations for data editing require sophisticated computer programs for operation. At a price of say 99,000 - $6,000, the editing alphanumeric terminal is an attractive proposition for use in a broadcasting control system. iith this unit, operations schedule data could he entered into storage as it comes to hand, if memory space permits. Last minute changes could be made by requesting a "page” of the schedule, editing it and then sending it back to the disc store. This method uses comparatively simple programs, by comparison with a conversational editing system. A. more expensive type of display terminal is the graphic display unit, costing above 55,000. It operates by controlling the beam position in a manner similar to that in an oscilloscope, raIdler than using a television raster. Its use lies in presenting data in pictorial or tabulated form and is often used in conjunction with a signalling device 10 called a light-pen, or position-indicating pencil. This can be used to indicate a specific set of co-ordinates on the screen, and so can be used, for example, to select one of a multiple choice question displayed on the screen. G-raphic displays could be used to portray information such as networking configurations in broadcasting operations, but it is probably not justified except in very large broadcasting centres such as ITHK in Japan. 192 - 5.6 hhVIhw Of CUnrhATb dYoThk figure 5-13, located in a pocket at the rear of the thesis, shows a block diagram of the computer-controlled presentation system. The essential link is the interface which has two functions : it provides a path for data communications between the computer and the operator, and it transcribes digital codes generated by the computer into control signal to operate the broadcasting equipment. Only one central processor and subsidiary disc unit are shown. To increase availability a second system could be connected to the interface bus system. This could operate in duplex, enabling comparison tests to be made in the hope that errors will be detected. Alternatively the second system could carry out off-line jobs such as inventory storage, provided sufficient back-up memory is available. Alphanumeric terminals are used for system control operator interaction and for operations schedule editing. A teleprinter is used to compile a log of deficiencies in the broadcasting operations. 193 - JKAPTER 5 - REFERENCES 1 P. Van der LELY and G. MISSRIEG;jER, "Audio Tape Cassettes,” Philips Technical Review.Vol. 31 No. 3, 1970, pp 77-92. 2 A. J. FORTY, "A Photographic Technique of Sound Recording- on Class Discs," The T elecoimnunication Journal of nstralia. Vol. 10 ho. 1, June 1954, p 22. 3 Ibid., p 25* 4 A. J. FORTY and F. A. MILNE, "The British Post Office Speaking Clock Mark II," Telecom. Journ, Aust., Vol. 10 No. 1, June 1954, p 2. 5 A. R. RuD-KEA, "The New Post Office Speaking Clocks," The Post Office Electrical Engineers1 Journal. Vol. 56 part 1, April 1963, p 1. 6 E. F. SaNDBACK, "Installations in Australia of the British Post Office Speaking Clock Mark II," Telecom. Journ. Aust., Vol. 10 No. 4, June 1956, p 108. 7 C. J. EATON, "Delta Modulation for Sound-Signal Distribution : A Ceneral Survey," BBC Research Department Report, No. 1971/12, p 1. 8 J. A. OREEFkRS and K. AIRMENS, "Code Modulation with Digitally Controlled Companding for Speech Transmission," Philips Technical Review. Vol. 31 No.11/12, 1970, p 340. 9 KENJI HAY^SHI, "PCM Stereo Recorder," NTiK laboratories Note. No. 134, March 1970, p 5. 10 EDJIN L. JACKS, "A Laboratory for the Study of Graphical Ian-Machine Communications," Conversational Computers, ed. JILLIAM D. ORR, (New York : John Wiley, 1968) pp 145-146. 194 - CHAPTER 6 STUDIO BROADCASTING- OPERATIONS 6.1 PREPARATION OP ITEMS POR PRESENTATION 195 6.1.1 Live Items 195 6.1.1.1 The Identification Signal 196 6.1.1.2 Line-Up Tests 206 6.1.1.3 Cueing Signals 208 6.1.2 Pre-Recorded Items 210 6.2 ON-AIR COMMENCEMENT 212 6.2.1 Presetting Operations 213 6.2.2 Sequencing the On-Air Operations 215 6.2.3 Programme-Line Signalling 219 6.3 OPERATIONS DURING BROADCASTING 223 6.3.1 Silenced Detection 223 6.3.2 Time-Flow Control 224 CHAPTER 6 - REFERENCES 226 - 195 - CHAPTER 6 STUDIO BROADCASTING OPERATIONS 6.1 PREPARATION OF ITEMS FOR PRESENTATION There are three tasks to he performed, prior to the start of the item’s transmission. These are: (a) identification, (b) engineering tests of source equipment and signal path quality (called the "line-up"), (c) cueing to cause item start at the correct time. Of these, identification and cueing could be automated whilst line-up could be performed manually or automatically, depending on the source. 6.1.1 Live Items Both identification and line-up signals are generated at the source and transmitted to the computer along the programme signal line. The main reason for identifying live items is to ensure that changes of source have not occurred without the information being relayed to the computer. The cueing signals such as those indicating readiness to test identification and line-up and signals starting the transmission of these signals are sent on separate cueing lines connecting each source with the computer interface equipment. The identification could also have been sent on a cueing line, but it is easier to use the existing signal switching equipment at the central control area to route identification and line-up 196 - signals to the appropriate decoding units. 6.1.1.1 The Identification Signal The identification signal comprises a unique number represented by some form of binary digits. The form of representation must be such that the number can be generated and transmitted in a simple manner to the computer for comparison with the schedule-stored identification number. It must also be easy to 3tore the code on magnetic tape and to recover it. After generation or recovery the code is transmitted along a single line, so the code must be in serial form at this stage. For storage at the generating and receiving ends a parallel form is better, so serial-parallel conversions are required. This can be obtained using shift registers. Whilst the simplest type of signal to transmit along lines is a d.c. level, it is easier to transfer sine wave tones through audio amplifiers and recover them from magnetic storage such as a tape recording. Since the voltage recovered in a magnetic replay head is the derivative of the recorded field it is simpler to recover a tone than a d.c. level. If d.c. is used either a "return to aero" (RZ) or "non-return to zero" (RRZ) recording current can be used for magnetic recordings. RRZ is more economical in flux reversals but does not have a self-clocking (i.e. a serial-signal timing indication) characteristic. Since the number of bits to be 197 - FIT, £- / identification - smL MEWML 198 - recorded is small the RZ system which is self-clocking is to be preferred. If tones are used then narrow-band (notch) filters can be used to detect the digital signals. Three anharmonic tones of 3, 5 and 8 K Hz could be used as the start/stop synchronising signal, the "zero” signal and the "one" signal respectively. The transmission speed would be slow but this is not important since only a few bits are sent. To generate the identification code in the first instance a manual selection system such as a group of thumb wheels can be used. These are sequential devices generating a BCD code (8-4-2-1) as a number 0 - 9 is selected by the setting of the wheel. For this encoder an octal digit (made up of three bits) can be extracted from each thumb wheel, the particular identification number being notified to the operator in radix - 8 form. Figure 6-1 shows a design of an identification signal generator in block-diagram form. The thumb wheel settings are transferred (in parallel) to the flip-flops (bistable multivibrators) of the shift register. The serial output of the shift register controls the gating of 5 or 8 H Kz bursts to the programme line, the bits being transmitted at a 200 Hz rate. Fifteen-millisecond bursts of 3 K Hz tone are inserted before and after the identification as start and finish indicators. The form of the complete signal is shown as the bottom-most waveform of figure 6-2. To describe the unit more fully, assume that the IDE^r (JjDl'-\oio° /V~4- 4-O^Szl oaAT s^for:__ C/.OCK UiNTfijOL. CLOCiC 6-A7ZT off__ ^//i/r (£) cjjP-i&oe V o/p -2_ ^yfrzn__ /7&£-£ /DEKUIMIM C-ENERATOC WM£F0M$ 200 identification number is 10100 (or 24 in radix - 8). The bits transferred from the thumb wheels are numbered 0 to N, so N = 4 in this example. When the "start” command is given two one-3hots (monostable multivibrators) are triggered. One develops a fifteen millisecond pulse which is used to generate the 3 K Hz start indication and to gate the transfer of the thumb wheel settings to the shift register. The other develops a longer pulse, the duration of which defines the start burst to the completion of the identification bits. For IT = 4 (5 bits) the duration is (15 + 5 x 5) milliseconds, i.e. 40 milliseconds, since each bit is five milliseconds long. After fifteen milliseconds, the "15 m Sec" one-shot switches off, removing the 3 K Hz burst and causing the Clock Control flip-flop to become set, since the "long-pulse" one-shot is also set. This flip-flop starts the Clock and "arms" the gating of the 5 and 8 K Hz bursts by the shift register. After a delay the Clock gate allows clock pulses to be sent to the shift register, and each five milliseconds the bits are shifted. Each bit from N to 0 arrives at the serial output (labelled ) and gates either the 8 or 5 K Hz oscillator to the line. After forty milliseconds each bit has selected a burst, and the "long-pulse" one-shot switches off. This causes the Stop Control flip-flop to become set, which after a short delay stops the Clock by resetting the Clock Control flip-flop and also triggers the 15 m oec" one-shot again. another fifteen millisecond burst 201 U-DtK rc Qi/^Pvr&z. XC - X/Hif. (JOVsTHN T p<£L - btJLfK-f FIE. & ~3 IDENTIFICATION-SIG-HAL RECEPTION 202 of 3 K Hz tone is gated to the line as a "finish" indication and the Stop Control flip-flop is reset. When the "15m Sec" one-shot switches off this time the Clock Control flip-flop is not set, because the "long-pulse" one-shot is switched off. Figure 6-2 shows the waveforms of the major blocks of the identification generator unit. At the time that the source wishes to perform an identification test the computer switches the particular programme line to the identification receiver (decoder) unit. A block-diagram of a design for this unit is shown in figure 6-3 and the corresponding waveforms are shown in figure 6-4. The unit performs the reverse action to that of the generator (encoder) unit. 8 and 5 K Hz notch filters detect the presence of a "one" or "zero" and the 3 K Hz bursts are used to begin and cease the shifting of the identification bits into the shift register. In detail, the 3 K Hz filter detects the "start" indication but until this signal has been present for ten milliseconds no action is taken. At this juncture a ten millisecond one-shot is triggered. When the fifteen-millisecond 3 K Hz burst is completed the filter output drops and the Clock flip-flop is "clocked". Since the "data" input is set by the "10 m Sec" one-shot the Clock flip-flop is set. However the "reset" signal will not occur because the 3 K Hz filter output and the Clock flip-flop true output (x) are not asserted simultaneously. - 203 - I PENT code - idioo N- +- W iKPz PturFL o/T — (C ItvPuf clock 0 'NPut- P/p ' &&— , A <^>«r < (loof/i} UlOC Mie Eff *— k k 1 V iWzn skh Mm 'nn \ I [KENT S iLNM- m /# JX pjp o oorfur j '—L ^ O pjf i cotPor (\L P/FX duTTcJr (Kj. P/Fl OoTfuf /*J. p/p <(- cto rfor (y\ /7£. IDENTIFICATION H£C£/j/£X WA^miS - 204 - The Clock flip-flop switches on the Clock which produces its first clock pulse about 2y milliseconds later. This timing causes the shift register to sample each identification bit near the middle of the burst. The 8 and 5 K Hz filters drive the “set" and "reset" inputs of the Signal flip-flop respectively. The true output (x) of this flip-flop is shifted into the serial input of the shift register by the clock pulses. At the completion of the identification the 3 K Hz filter detects the "finish" burst, and since the Clock flip-flop is set, the "Reset" one-shot is triggered. This develops a twenty millisecond pulse that resets the Clock flip-flop and turns off the Clock. Thus the shift register stops with the first bit received shifted to flip-flop N. The parallel output of the shift register (shown at the bottom right corner of figure 6-4) is now ready for use by the computer, and this is accordingly signalled by the "Reset" one-shot pulse. The "reset-pulse" could be used to interrupt the computer’s operations (according to a priority scale) and commence the operation (or "running") of a program which tests item identification codes. The parallel-stored, "received" code would be read into the computer’s memory via the interface equipment and a comparison made with the identification code listed in the schedule as associated with the source. There are four possible conditions arising from the information received on source and identification code: (a) the source is correct (i.e., it is scheduled for use) but - 205 - the identification code is wrong, (b) the identification code is correct (scheduled for use) but the associated source is wrong, (c) neither source nor identification code are scheduled for use, (d) source and identification code are mutually correct* The responses of the automation system to the discrepancies of (a), (b) and (c) depend on the sophistication of the identification testing program. A simple routine might merely report that a discrepancy exists, giving the source and identification code received. A more useful routine might also search the operations schedule for other references to the received identification code or for use of the source at a time near that at which the identification code was received. In the case of (b) a re-allocation of sources could be performed automatically to remove the discrepancy. However, there could be a risk that later schedule entries would be upset unless a sophisticated resources-allocation program could be run. If a successful identification code test has not occurred by a certain time before broadcasting (say five minutes) then a warning message should be printed to inform the operations staff of the problem. This should allow sufficient time to correct the situation, either by a correct identification test or by overriding the test if some malfunction (technical or administrative) is responsible. When condition (d) occurs, - 206 - the scheduling of this warning message is cancelled. The message could be initiated by placing an event within the operations schedule or by a special time-controlled executive program (a "real time executive" possibly supplied by the computer manufacturer) which schedules such alarms. 6.1.1.2 Line-up Tests Engineering tests are performed to ensure that equipment is functioning satisfactorily and to establish an agreed datum of signal amplitudes. For live items the equipment consists of units used within the source, such as microphones, gramophone turntables and tape replay machines, and the transmission line and associated amplifier linking the source with the central switching area. It is probably not worthwhile to automate the testing of source equipment because of the diversity of units and connections within each source. The microphones are most easily tested using the human voice, and reproduction equipment performance can be approximately gauged by replaying typical material. Testing could be completed locally at the source if a technical operator is in attendance, or by co-operation with technical staff in the central switching area if a one-man announcer system is to be used. Automated testing of the programme line and associated amplifiers could be implemented using a similar method to the identification system just described. Parameters of the - 207 - communication channel which could be tested simply are: (a) gain, (b) distortion products due to non-linear transfer characteristic, (c) frequency response, (d) signal/noise ratio * The gain and distortion could be measured using a tone (say 1 K Hz) transmitted from the source. The signal/noise ratio is measured by establishing a reference level (say with the 1 K Hz tone) and then removing the reference and measuring the residual level. A sequence of tone bursts at different frequencies (called multiburst) could be used to check the frequency response at spot frequencies. The line-up signal generator would consist of a number of oscillators which are gated to the programme line, according to the requirements of the test being performed. For example, the test could commence with 1 K Hz tone for gain and distortion measurement, followed by no tone to enable signal/ noise measurement. Finally a sequence of tone bursts at 50, 100, 400, 2 K, 4K, 8K and 12 K Hz would spot test the frequency response. Control of the generator would be similar to that provided for identification transmission. A "ready for line-up" signal sent via a control line to the computer would cause the source*s programme line to be connected to a line-up signal testing unit situated in the central switching area. A "start" cue would be sent to the signal generator at the source, and 208 - this cue would start a "clock” pulse generator which switches the test tones to the line in sequence. Upon reception of 1 K Hz tone the testing unit would commence a series of tests to measure amplitudes, distortion products and noise level. Distortion is the most difficult to measure since a notch filter must be adjusted in frequency to remove the 1 K Hz reference tone. This could be done automatically using feedback control to give minimum output signal energy. Each value determined by the testing unit could be signalled to the computer, where a line-up test program would process the results. All results would be logged on a hard copy printer and if results are outside prescribed limits, the operations staff would be notified by a printed message. The amplitude measurement could be used directly to set transmission path gain, either through voltage control of amplifier gain or by a stepping motor controlling a potentiometer. Also, the multiburst results could be used to adjust the frequency response (i.e., to "equalise” it). However, the implementation would be more complicated because it is a multi-variable problem. 6.1.1.3 Cueing Signals The cueing signals required by live sources are the identification and line-up request and control and an on-air indication. As live items are expected to finish on time, no "item concluding" cue is needed by the broadcasting control 209 - system.. To reduce the number of operations and the number of cueing lines needed the identification code and line-up signals could be amalgamated to form a single sequence. Thus a single line from the source to the computer interface would request an identification/line-up test and a second line from the computer would grant the request and commence the transfer. Savings could also be made by rationalising the designs of the generating equipment and the decoder/testing equipment. The on-air indication could be derived directly from the source-to-transmitter switching unit. It could take the form of a single signal which is a logical OR of the outputs selected to receive the source. Alternatively each transmitter feed selected could be indicated separately, so the studio operations staff would have confirmation of the configuration of the switching system. A warning signal given perhaps 30 seconds before item commencement could be supplied from the computer. This could be scheduled using a similar method to that used for identification test default. A test for studio occupancy could also be useful, to ensure that the studio is manned. This could consist of a buzzer or lamp call within the studio, initiated by the computer say five minutes before the studio commences operations. If a replay signal is not received within two minutes, an alarm message is printed for action by operations staff. Upon receipt of a reply the computer would acknowledge by 210 - turning-off the call signal. This test would be useful in systems where live item identification and line-up testing is not used, but is otherwise redundant since the call for identification test indicates occupancy. The cueing signals can be d.c. voltages controlling logic gates and can be transmitted over long distances providing suitable driving current and line impedance are selected. 6.1.2 Pre-Recorded Items As with live items, pre-recorded items require identification, engineering tests and cueing signals. The concentration of tape reproduction units as a separate group to the live sources enables a greater degree of control by the computer-controlled broadcasting system. Savings in equipment and staffing can also be effected. Each recording on tape is preceded by a leader which contains the line-up tests and identification code. The line-up would include two extra tests: (a) tape replay speed, (b) wow and flutter measurement. The replay speed would be assessed by checking that the i initial tone was 1 K Hz and not say, 500 Hz or 2 K Hz. Incorrect selection of speed would cause the computer to cease further testing and request the tape preparation operator to remedy the error. Wow and flutter measurements 211 are made using a 3 K Hz tone, the measuring equipment being incorporated in the computer*s line-up tester. To prepare a recorded item for replay the selected tape is laced onto a prescribed replay machine. The allocation would be determined either by a resources-allocation program running in the computer or manually by an operations supervisor. When the operator presses a "ready for test" button, a register associated with the source requests service, identifying itself to an intermediate buffer unit which concentrates requests to the computer. The replay motors of the machine are started by the computer and the line-up test and identification code are transmitted to the computer for 2 processing. The identification code could alternatively be recorded on a second track, the cueing and control track, and be passed to the computer via the intermediate buffer. When the tests are completed the tape is stopped by a cue on the tape marking the start of the item itself. The "stop" command could be processed locally within the tape replay unit or handled by the computer. An indication should be given to the computer that the item is correctly cued for replay. If this is not received within a certain time interval it is likely that the cue mark is missing, and operator intervention must be requested. If the tests are completed satisfactorily the operator should be informed, either by lighting an "OK. for air" lamp or by a printed message. If not, the failure could be caused - 212 - by one of a number of faults. For example, the tape transport (motors or tensioning system) could fail to operate properly, the identification code could be received incorrectly, the line-up tests outside tolerance, or the cueing operation fail. If, in fact, the wrong item has been selected, the correct one must be loaded onto the same unit. Otherwise another unit, selected as a substitute by the computer*s (or supervisor*s) allocation system, must be used and the faulty unit taken out of service.*^ Minor items stored on cassette or cartridge could be handled in a similar manner, although some modifications might have to be made to commercial multi-cassette or cartridge replay units to incorporate the testing system. In the case of short announcements a simpler restricted identification code could be used. 6.2 ON-AIR COMWCjSMMT Several tasks must be performed near the time that an item commences broadcasting. These include: (a) pre-selecting (presetting) the new configuration of the switcher, (b) cueing and pre-rolling items, (c) fading and mixing, (d) switching and confirming switcher operation, (e) receiving information such as cues and identification from remote sources, - 213 - (f) scheduling the next switching event. With the exception of cueing, the operations can be scheduled by reference to a specific event such as the execution of switching. Switching itself would be scheduled at the previous switching event by referring to the operations schedule, 6.2.1 Presetting Operations In addition to the on-air switcher configuration and "30-seconds" warning cues mentioned in section 6.1.1.3, a preliminary indication of the next switcher configuration can be arranged by using a presetting operation. Presetting has two uses: (a) to delay actual execution so that several manual operations can be synchronised, (b) as an indication to inspire the confidence of human operators in the process about to be performed. Switcher execution controlled by an electronic digital computer is fast enough (compared to the time scales within broadcasting) that presetting for synchronisation is not required. However, its use as a pre-checking function is very desirable, particularly during the period of introduction of automation into broadcasting station operations. Presetting can easily be designed into switching hardware, the main requirement being a memory element at some point to store the preset data. The data could then be "echoed" to manual operations points in a similar manner to the on-air 1/ D/Kec t/d n OF t im ef c o^ fig T&rfot CiMMovCt T&Tsoa^pot fte-KGuC swtrcH/tiG- , COMflGNOS ts PfiQ//Oos i sokzout-L C (ff fh-FD UDN SUCCEW (if- Frhf WACcz swim if Ji £T/ycx M^y fui^ Sk/rrcHlVf- acczw C p/fAsf Aeqo £Vavr a itxr N€XT PfPC SUy/rzH l < M£~ au 10€NT UP iol evosr- o/chn £V£7vf~ d &Q\ eYeN/ ) ^ > ) aj of t N- - - mmm 214 - omnoFs c PiX.fi EXTRACTED TtMe n oris iN'mwki- schedule FKOF - 215 - switcher configuration. The presetting operation could occur immediately after the previous switching operation or be delayed until say ten minutes before the next event, 6,2,2 Sequencing the On-Air Operations The procedure followed when a switching event is executed is illustrated in figure 6-5. The operations listed at the start of section 6.2 are performed, although not necessarily in the order shown by figure 6-5. The location of the test: “that successful identification has occurred” is dependent on whether the source is accessible or not. Also, the pre-roll time might be only one second or less, so that "commencement of slow fade” would precede the "pre-roll” task. To initialise the presentation sequence, operational time (true time) is compared to the time-values of successive entries in the operations schedule until the next event to occur is located. Then the present activity, determined by the previous event, can be implemented if it is necessary to correct the state of operations. With the broadcasting control system now operating, the sequence is initiated at the completion of the previous event. The operations schedule is accessed to extract details of the next event. The next event time is used as the datum for scheduling the various tasks performed before and after the switch. Each succeeding task is scheduled at the completion of the previous one, the scheduling process requiring the - 216 - commencement time to be calculated, and the commencement time and task location in the computer memory to be registered within the real-time controlling software♦ as well, the operational data is moved from the schedule to the data area of the task. The real-time controlling software is a computer program either written explicitly for the particular broadcasting control system, or supplied as a standard program by the computer manufacturer. Its main use is to schedule (i.e., register for action), start execution ("run”) and stop execution of specific task programs stored in the computer memory. The scheduling consists of taking the commencement time value of each task to be run and comparing with the computer*s clock reading. When the time values are equal the task is allowed to take control of the computer for a certain time, say 1/50 second, after which the real-time ’’executive” again asserts control. The task can be allowed to proceed, or another task, with higher priority which also requires execution can be given control. By allowing dynamic control of priorities the ’’executive” can effectively allow several programs to run. This is called multi-programming. In addition, operator commands from a keyboard entry device can also influence "executive” operations. Except for confirmation, the tasks indicated in figure 6-5 have been described in previous sections (scheduling in section 5.3 and the others in 5.4). When the switching task - 217 - is commenced a signal is sent to the switcher via the computer interface to implement the preset-selected cross-points. After allowing sufficient time for the previously operated cross-point for each destination to release and the new selection to operate, it is desirable to confirm that the correct cross-points, and only those, are selected. This can be achieved during the interval after switching and before the fader is opened. To perform the test properly a signal which identifies the switcher input selected for each output must be passed along the programme-signal path. The signal received is then tested to confirm that the desired switcher state is set. A possible signalling method would be to send a voltage pulse along each input in sequence and, by measuring the delay time of the received pulse(s), determine which input(s) is (are) operated. This can be accomplished using shift registers, as was done in section 6.1.1.1, to move a signal representing a "one" to each input in turn and to store any signals which pass through to the output. If the same clock pulses switch the input signals and shift the output connection to successive bit positions in the output shift register, then the final bit pattern in this register will show which inputs, if any, are selected. It is probably better to have a separate shift register for each output, although it would also be possible to switch each output to a single register. The testing signal would preferably be a d.c. voltage, if the switching circuit 218 - can pass this; alternatively a tone could be used as in section 6.1.1.1. The checking process compares the bit patterns with a desired state table (also a bit pattern). The bandwidth of the switching path would be sufficient to complete the test quickly, so that several attempts to switch could be made if the initial one failed. This system, although costly to implement, has the advantage of being usable with any switching method incorporating a temporary disconnection (e.g., a fader) in the output feed. A cheaper alternative can be used in cases where physical contacting devices such as relays are employed. An extra set of contacts can be used to indicate that at least this pair of contacts has been closed or opened by the switching signal. The system is not foolproof since the signal carrying contacts are not tested, but by making the confirmation contacts the least reliable (e.g., by carrying heavier current and poor position in magnetic field) a reasonably safe test can be applied. One problem associated with the period just before on-air presentation is that late changes to the station broadcasting programme occasionally are requested after the affected event has been scheduled. If the modification is entered into the operations schedule by the normal method it will not be effective since the next event data has already been extracted. One way of surmounting this is to assume that any editing performed on the schedule has affected the next event, and to re-execute the next event-scheduling program. This would reset 219 - the task sequence and timing, according to the nature of the modification, and run any tasks advanced past the present value of time. If, however, the change gives less than three minutes warning of switch execution it is better to handle the change differently. An alternative method is to allow direct changes of the data stored for each task to be performed. The changes could be entered by mechanical units such as thumb wheels or switches, or by typed messages which include the data, on a keyboard. A separate data-changing program would need to be run to store the new data. 6.2.3 Programme-Line Signalling On occasions the only suitable means of communications is the programme line feeding the item from the source, and a brief discussion of this was made on pages 34 and 35 (section 1.4.3). The types of messages likely to be sent include short duration signals such as identification and cueing, intermittant signals of low information-rate for remote control of equipment, and high information-rate signals for data transfer and voice communications (termed "talk-back”) between operational staff. Since almost the entire range of audible capability of the programme-carrying channel is used, it is difficult to share it between programme and communication signals without the latter being discernible by listeners. A number of tests have been performed (including those by CBS and by the BBC, discussed below) to determine the types of channel sharing which are 220 - least objectional and, hopefully, subliminal to discriminating listeners. The tests have centred aroud the use of low level-short duration hursts of tone, or frequency notches at some point(s) within, or at the edge of the hand. CBS has developed a signalling system called "NetAlert” which uses low level tone hursts; of frequencies between 1 K Hz and 3.5 K Hz. According to subjective tests which CBS made, hursts of tone of 30 milliseconds duration of frequencies between 1 K Hz and 3*5 K Hz and of level - 20 dB were unobtrusive^ (but presumably audible). It was reported that rythmic music could mask the tone completely. Magnetic tape reproduction has in the past tended to suffer from short duration signal losses, called dropouts. Considerable research has been carried out into the causes and effects of dropouts, and has included work on audibility and estimation of annoyance. Workers have reported that dropouts (which could be considered either as a method of signalling or as a preparatory step to inserting signals) of duration less than 10 m.secs are inaudible, whilst the annoyance value of dropouts in the range 50 to ,100 m.secs varies strongly with duration. ^ The B.B.C. has recently published a feasibility study on simultaneously subliminal signalling. This is a comprehensive report which considers the possibility not only of exploiting loudness contour effects (vide thesis section 1.4.2, page 25) 221 and masking (section 1.4.2.2, page 30) but also reverberation and Ohm's lav/ of phase (section 1.4.2.1, page 27). Experiments were performed on four systems : (a) quantisation, relying on the ear's frequency analysing characteristic (as do vocoders), (b) reverberation, (c) attenuation (amplitude dropout, and also insertion into dropout), (d) frequency notch signalling. Of these only the last three showed promise. The attenuation signalling method required slow transmission rate (2 bauds) and specially shaped dropouts of 1 to 2 m.secs. The reverberation method had higher sending rates (50 baud) but apparently a satisfactory detection system is not yet developed. Frequency notch signalling was suggested the most practical with sending rates up to 40 baud. A use of programme line signalling which is applicable to computer controlled broadcasting is the reception of identification and item commencement and conclusion cues from otherwise inaccessible sources. To assess the feasibility of ihis method I have carried out tests on the audibility of dropouts, and tone signals with broadcasting item material. The recordings and listening tests were carried out during the first half of 1969 at the University of New South Wales and a report on the experiments is included in this thesis as Appendix A. The tests investigated three factors : 222 (a) the use of insertion-into-dropouts (gating), (h) mixing the signals* (c) the effects of superimposed noise as a mask* The results indicated that insertion into dropouts of 10 m.secs are definitely noticeable, and 5 rrwsecs bursts are also detectable. Superimposed (mixed) signals were less noticeable, even the 10 m.secs bursts, provided the relative level was -30 to -35 dB. The use of noise did not lessen the annoyance of the bursts. The use of method (a) of my tests is feasible for short duration, precisely time-located signals such as remote item identification. Otherwise problems of detecting the presence of a signal occurs. For very simple cueing such as a signal to commence a unique pre-arranged operation, a notch of small bandwidth could be used. The sending rate would be very slow, but this would be acceptable in cases such as the cueing of a source switch to or from a sporting event. In this situation the cross-over time might not be well-defined, so manual cueing would be necessary. It would be advantageous to the commentators if a simpler non-off" cue were available. A final point to consider is the problem of cueing information being recorded along with the item, and on later replays, giving false information. Possible solutions are : (a) to delete the cues if possible, (b) to send the cues at a time when they will not be recorded (which is restrictive), (c) to identify the cues in some way - 223 Probably the simplest method is to not record items at locations remote from the source. However, outside broadcasting could be an excaption, but if a frequency notch is used, this cue could easily be deleted. 6.3 OPERATIONS DURING BROADCASTING Operations which are carried out during the broadcast include monitoring for faults and quality, last minute changes to schedules to control the synchronisation of protime to true-time, and emergency action. 6.3.1 Silence Detection. The simplest form of automatic monitoring is to detect that no signal is being transmitted. The difficulty in performing the task is to determine what power level represents "silence" and what interval of silence represents a fault condition. For example silence of twenty seconds could be acceptable in a classical music performance, but not during a nev/s broadcast. Also, frequently musical items contain long passages of low level. In manual monitoring systems the silence alarm signal sounds but the operator simply ignores it. The advantages of computer controlling a silence detector is that it is possible to vary the "level of silence" and the "period of silence". One method v/ould be to have selectable level-thresholds but to fix the time constant to, say five seconds. When five seconds of "silence level" is detected, the situation is signalled to the computer by interruption or 224 by a raised flag which is scanned by the computer. The computer counts the number of consecutive 5 - second time indication on the particular signal line and if the count exceeds the "period of silence" set for the particular item being broadcast, takes emergency action. This could include the replay of a tape containing an apology and the use of fill-in music. The computer could also test different points in the signal path to isolate the fault. 6.3.2 Time-Flow Control One of the problems in the assembly of a network programme is that the replay durations of recorded items do not have a better accuracy than - 0.5$* This is not only caused by variations in replay speed, but also by elastic and non-elastic changes in tape dimensions. The value of - 0.55^ represents an uncertainty of - 9 seconds in a half-hour duration item, which is unacceptable (section 3*3*1 )• The solution adopted by motion-picture and television recording systems is to record on a second track a sample of precise frequency tone called pilot tone. During replay the capstan drive-speed is controlled to obtain the correct frequency of pilot tone. An alternative system, mentioned in section 3.1.2.2, is to record marks at regular time intervals on the tape. This method can be extended, by using a set of unique numbers which are placed on the tape at the time of recording, with spacing of 1 second, say. The rate of reproduction of the numbers can control the replay timing, and by sampling the code replayed at a 225 - particular instant and comparing it to that noted at the beginning of the replay the computer can measure the time-lapse of protime compared to true-time. If an emergency such as the failure of a tape splice occurs, the computer control system could adjust the position of the recommencement of the item to still finish at the correct time* Splicing of different tapes would cause a discontinuity in the number scheme, but this could be accounted for by comparing adjacent numbers and up-dating. Such number systems have been used in video tape automatic editing systems. The measurement of protime lapse could also be used to correct mis-synchronisation between networks about to exchange items. However variation of replay speed to achieve this is a delicate proposition because of the ear's sensitivity both to pitch changes and to absolute pitch. Possibly the solution would be to correct spoken word items in this fashion, but not to interfere with the item requires precise pitch reproduction, e.g., musical items. This method would correct incremental errors of a few seconds only since only small pitch variations and wow can be tolerated. CHAPTER 6 REFERENCES J. HILLER and A. S. GRAY, "The Use of Computers to Control Operations of Broadcasting Studios and Transmitters, Report Number 1, submitted to Controller of Technical Services, Australian Broadcasting Commission, 1st August 1969, p 22. Ibid., p 21-22. Ibid., p 23-24. A. A. GOLDBERG et al, "The CBS NetALERT - A System for Network Signalling," IRE Transactions on Broadcasting;. PGBC - 7 No. 3, August 1961, p 43. B. L. CARDOZO and G. DOMBERG, "An Estimation of Annoyance Caused by Dropouts in Magnetically Recorded Music," Journal of the Audio Engineering Society. Vol. 16 No. 4, October 1968, pp 427, 429. P. C. J. HILL, "Simultaneous Subliminal Signalling in Conventional Sound Circuits : A Feasibility Study," B.B.C, Research Department Report. No. 1971/1. JOHN G. McKNIGHT, "Speed, Pitch and Timing Errors in Tape Recording and Reproducing," Joum. AUD. Eng. Soc.. Vol. 16 No. 3, Inly 1968, p 268. - 227 - CHAPTER 7 CONCLUSIONS 7.1 COSTS The costs of the control computer are about $60,000 for a small process control computer with disc, 16 K of memory, paper tape reader and display terminals. To this must he added development costs such as the design and construction of interface units between the computer and the broadcasting equipment, and the writing of specific computer programes to control operations in the particular station. The development time needed to automate station presentation operations in a small, single network system would be 5 to 10 man-years of hardware and software design, plus technical support staff. Other expenses which could be incurred in introducing automation are the transfer of a record library to tape, and restructuring of station programme scheduling staff to match the computer storage and editing system, 7.2 BENEFITS The two main benefits are the reduction in presentation errors, particularly important in commercial stations, and a more even standard of operations. Introduction of automation gives an opportunity to re-appraise methods of operation, and antiquated procedures can be modernised at the time of change to automation. The system of storing of future operations schedules within the computer's memory, makes information 228 - distribution and ensuring up-to-date copies easier, provided that back-up precautions are taken to avoid a fault condition destroying the work of many weeks. Staff savings can also be made if the areas of influence of automation are chosen carefully. However, piece-meal adoption of automation in a few sections will not benefit staff costs and should not be undertaken except to prove the validity of automation in the station as a whole. Once computer control has been introduced, additional tasks such as automatic editing of tape items and stores inventory can be added later for reasonably low extra cost. Experience in operational methods which is useful for later expansion to large resources control automation systems such as "TOPICS'* at NHK will also be gained. APPENDIX A IN-BAND SIGNALLING- - 1 - (l^o) APPENDIX A In-Band 3ign al 1 in/-,aidi b i 1 i t y Tests (a) Possible Uses. The use of signalling between network centres and between a network centre and its regional transmitters is desirable both, for control and information transfer purposes. Dome examples are: (i) the identification of programs originating at other primary centres, in the cases where identification testing prior to the start of the program is impossible, (ii) the interchange of data between primary centres. An example is the updating of programming information to the supervisors at each centre in the case of late changes. This comd be an alternative to the use of transmission lines as order wires when this use is not possible, (iii) t e control of switching at regional centre studios and the control of transmitters. For example, cases where switching is at present performed in the local studios could be remotely controlled. The logging of transmitter parameter data and initiation of data transfer telephone calls could be signalled by the computer, and the transmitter could also be switched on remotely. (b) .Am of Signalling The aim is to transmit data and control signals on broadcast lines with the constraint that these signals be non perceptible to listeners. ( 2 V) (c) Cnoice oi oignalling j e uhod Four possible methods of transmitting signals on broadcast transmission lines are: (1) Frequency-shared, out-of-band signals (2) Frequency-shared, in-band signals (3) Time-Shared, in-band signals (4) Superimposed program and in-band signals. There is also, of course, the time-shared out of (time) band method which is the use of lines as order wires when they are not for program use. This restricts data transfer to a few times a day, and could not be used to transmit control signals. Of the above methods only (4) does not interfere in some way either with the frequency domain or time domain available, lie t hod 1 This method has the advantage that there is little likelihood of noticeable loss to the "average" listener, however, unless the out-of-band signal spectrum is placed beyond the upper audible frequency or lower audible frequency, the method implies some restriction on the program bandwidth compared with available bandwidth of the line. Low frequency signals could not be used because of the slow transmission rate required with IF say about 1 bit/sec. as the bandwidth of present transmission lines is restricted to 15 K Hz, or less, method (1) implies a further degradation in program bandwidth. - 3 - (Z32 ) Method (1) has the advantage that signal detection is simple and the data transmission rate can he reasonably high, at the high end of the frequency band, Method 2 This method suggests the use of a narrow ’’notch” of frequencies within the audio broadcasting bandwidth. To be least noticeable the notch would have to be at least 120 Hz wide to achieve a reasonable data transmission rate and perhaps an even wider notch is needed. If 333 modulation were used a pulse rate of about 10 Hz would be possible. However, the higher the ’’centre” frequency, the more difficult it would be to realise the notch filter, since the Q would have to be higher. Method (2) causes some deterioration in the program transmission and requires a fairly sophisticated modulation- demodulation system. If the data rate is not required to be high, it could have some applications. Method 3 The term time-sharing means that for some intervals of time the program signal is deleted and the in-band data signal is substituted. In order to separate data signals from program, fairly precise synchronisation of suitable gating pulses is required, together with a (rather inflexible) pre-arranged transmission time schedule. A relevant problem is the audibility of such time-shared - 4 - (2 IS) si nal interruptions. I,lethod 4 By superimposing program and data signals via a mixer stage no part of the channel (either time or frequency) is "being used exclusively "by the data signal. The problem now becomes one of annoyance to the listener, together with the difficulty of separating the data signal from the program. (d) Some Previous Work Effects of Tape Dropouts Investigations by tape and recording equipment manufacturers (e.g., Ampex) have indicated that the degree of annoyance associated with dropouts depends on: (i) duration of dropouts (ii) depth of dropouts (iii) number of dropouts in close proximity (iv) the subjective reaction to the program material. the Iwcjzir In general*the dropout, the greater the degree of annoyance and similarly the greater the depth of light dropouts. Variously deep dropouts, while more annoying, all seemed to have about the same degree of annoyance. The manufacturers suggest that dropouts under about 20 m.secs, in duration cannot be heard (this was not found in the present tests). Masking of audio signals The masking of signals has been extensively investigated by acoustics engineers 2 34 FIG-. A-1 BLOCK DIAGRAM OFSIOKAL MIXING (no- 5 - The main properties are: (i) tones will tend to be masked by sounds of lower pitch (ii) generally the smaller the difference in pitch the better the masking with the exception that beats will occur as the difference vanishes (iii) narrow band noise centred on the same pitch will raise the threshold level (i.e., the level at which a slight increase in the signal would be perceived). (e) Investigation To assess the different signalling methods it was decided to carry out audibility tests on methods (3) and (4)* The data signal was chosen to be a burst of 1 K Hz square wave. This could represent either a pulse, in POH transmission, or the carrier when the 1 K Hz pulses are modulated as a binary code. To test method (3) a gating pulse v/as developed which allowed either the program signal or the data signal to be sent. This gating pulse also defined the "burst" of 1 K Hz square wave which became the data signal. A block diagram of signal generation is depicted in figure A-1. The width and repetition rate of the gating pulses could be varied as desired with a minimum width of pulse of 1 m.sec. In addition, the circuit was arranged so that a small set of bursts (say 3 bursts) could be inserted at random into the program signal. To test method (4) the gating amplifier associated with - 6 - (Hi) the program signal was changed to a mixing ("OR") amplifier. To generate the program signal monotone speech and slow organ music (Handel*s '’largo”) were recorded on tape. The combined signal output, after gating and mixing in an AD80 analogue computer, was recorded on one track of a stereo tape recorder. The second track was used to mark the position of the (randomly) inserted bursts of tone. (This introduced the possibility of cross-talk between channels during replay, but none was heard when silence was recorded and replayed on the program signal track)• In order to take measurements of levels, a standard VU meter and a storage oscilloscope were used. The VU meter was used to set audio levels of music or speech being recorded on the "output” tape recorder. It could not be used to set the level of the tone burst because of the rise time of the meter. To accomplish this, the brightness of the storage oscilloscope was set to a constant level and the storage property used to estimate an average amplitude of program audio, and the amplitude of the tone burst. From these measurements program-audio/tone-burst ratios in decibels (dB) were calculated. Thus, the program audio level was first set by the VU meter, and relative measurements were made using the oscilloscope. Variations in audio amplitude measurements depend on accuracy in setting the storage brightness. However, it is estimated that these variations would have little effect - 7 - (237) on values of program/tone ratio. The Experiments Equipment used: (i) AD80 analogue computer to provide gating and mixing amplifiers and also the logic circuits (multivibrators) to generate switching pulses (ii) .'’Advance" H1 square wave generator (iii) - 1 D. Tandberg 2-track tape recorder for replay of program audio signal - 1 Tandberg stereo, 4-track tape recorder for the recording of the combined signals (iv) 600 60 dB variable attenuator (v) VU meter (vi) White noise generator (vii ) Band pass filter, to restrict bandwidth of the noise (viii) Tektronix storage oscilloscope (an integral part of the AD80 analogue computer). The experiments performed were divided into three parts: (i) gating the signals (method 3) (ii) superimposing the signals (method 4) (iii) the effects of masking noise. In each case several values of audio/tone ratio were used, extreme values being 20 dB to 40 dB of tone below signal level. Tone bursts of 5 m.sec. and 10 m.sec. duration were used, with burst repetition rates of about 300 m.sec. The pulse frequency, 1 K Hz, and the repetition rate of 300 m.sec. lie F/£. k-?_ SHhPlHC- OF BURSTS OF IKFz PUlSFi - 8 - (^^9) at the most senstivie regions of aural perception, so the tests represent a stringent test. However, it is also possible that the 1 K Hz tone will tend to be masked by lower frequency sounds. Some attempt was made to "shape" the tone burst to reduce "clicks". The waveform envelope is shown in figure A-2. The "AMD”, or gating, amplifiers were implemented in the AD80 analogue computer by using multipliers. These have an error of the order of 1 °/> of maximum signal and so introduced clicks. To eliminate the clicks the amplitudes of the signal inputs were raised, and the output signal was attenuated to compensate. About 28 dB of gain/attenuation was used. In performing the experiments groups of tone bursts were both randomly and continually inserted into and superimposed onto music and speech. To examine the effects of noise mixed with the tone bursts, "white" noise from a noise generator was passed through a band-pass filter with a range of 900 Hz to 20 K Hz. This covered the frequency spectrum of the tone burst but had a reduced intensity because of the lack of lower frequencies. Results (i) G-ating (method 3) The burst insertions of 10 m.sec. duration are detectable, either due to perception of tone if the program audio is soft or to perception of dropouts if program audio is loud. The - 9 - f 14-0) 5 it.sec, duration bursts are much less noticeable but can still be detected. The relative amplitude of audio to tone is not very critical, provided the ratio is not too small, (ii) fixing (method 4) The perception of these tones depended more critically on relative amplitudes, than did the gated tones. In general the 5.m.sec. bursts were less noticeable than the 10 m.sec. bursts, but both were un-noticeable if the relative level was below 30-35 dB. This figure applies to both music and speech, listening tests were performed in a laboratory listening room, but only one observer has been used, to date. (iii) Effects of Noise The addition of noise did not lessen the annoyance, because of the high levels required to mask the tone. Also, the level required to "fill out" dropouts caused as much annoyance as the dropout itself. Conclusions It appears possible to use the superimposition method (method 4) to send data and control signals without disturbing the audience. In order to maintain a relative audio/tone levej. greater than, say, 35 dB, the tone level will not be far above noise level. However, recovery methods will in any case be rather sophisticated, to separate tone from program. Method 3 would almost certainly be noticeable to a discerning listener, but the short 5 m.sec. bursts are not severely so. Recovery methods are simpler, and the system - 10 - l 74l') might i'ind specialised use in the identification of interstate programs. To accomplish this bursts of about 7 rn.sec. duration would be transmitted during the first half second or so of the program. The time of program start would provide a precise synchronising point from which recovery gating could be timed. (f) Detection of Signals method 3 type pulses could be recovered by switching (gating) circuits provided the time of transmission of the pulse burst was known to, say, 1/10 cycle of pulse. If the information is encoded onto the burst in binary form, represented by the presence or absence of a pulse, then the recovered data signal can be stored in a shift register in a similar fashion to that used in the source register of the tape identification jjrocess. To recover superimposed signals (method 4) some form of correlation system is suggested, Essentially, this system uses integration methods to recognise a certain energy spectrum pattern, the signal being compared either to previous samples of the signal (auto-correlation), or to another, reference, signal (cross-correlation). If the information were sent as Pulse Code modulation (PCM), with a 1 K Hz wave as carrier, the simpler cross correlation method could be used with a 1 K Hz wave as the - 11 - f Z42) reference at the receiving end. The rate of transmission would be slower than for binary coding of the 1 K Hz pulses but the detection circuits would be more simple. - 243 - APPENDIX B PAPER: "FACTORS IN THE PURCHASE OP A SMALL PROCESS CONTROL COMPUTER" Submitted as Supporting Material - 1 - (Z44) factors in the Purchase of a Small Process Control Computer by A- S. GRAY. (Paper accepted by the Institution of Radio and Electronics Engineers Australia for publication in May, 1972 issue of The Proceedings of the Institution). To explore the possible advantages of computer control, the management of an organisation generally commissions a feasibility study. The objects of this study are to determine the nature of the tasks to be controlled, the economic advantages and the implications of the introduction of computers on the industrial process as a whole. If the results are propitious, and management decides to continue, the project will pass through the following stages: (a) selection of a suitable computer, (b) development of process controlling system to the point of setting it in operation, (c) maintenance of the process control system, (d) improvement and extension of the system. The success of each of these stages is largely influenced by the computer, which forms the hub of the system. Thus factors which affect each stage must be considered at the time of computer purchase. Selecting the Computer The findings of the feasibility study will indicate computer requirements in terms of process Input/Output (I/O), - 2 - ( 24$ ) character handling I/O, system response and the amount of data to be stored. The characteristics of both software and hardware of the selected computer will influence the operation of these. Process I/O is concerned with the passage of signals (data and control) between the computer and the industrial plant and with the requests for service from the plant. Salient computer characteristics for which data should be obtained are: (i) the number of separate devices that can be directly addressed using the I/O bus, (ii) the amount of loading the I/O bus can support without requiring some form of repeating unit, (iii) the maximum distance that a peripheral device can be located from the computer without requiring a repeater, (iv) the levels and method of transfer of signals along the bus, to assess compatibility with peripheral units, (v) the number of priority levels for central processor interrupt requests, and their relationship with the central processor priority status, (vi) the availability of interfacing units such as bus repeaters (and the number allowable), digital multiplexers, analogue-digital and digital-analogue converters, - 3 - (vii) the instructions which could be used to communicate via the I/O bus. Instructions which are useful with process I/O are those which clear or set bits in the computer word being processed or which shift bits within the word. Character I/O is used to read in data and control messages from system operators and to print out messages and logging details for operator information and action. The most important points here are the machine architecture and operating speed. Characters are often stored as 8 bit units so a machine based on 8 bits or multiples of 8 bits is likely to be more suitable. The efficiency with which characters are processed depends on the instructions which move the characters from one memory location or peripheral to another and those which compare characters. The speed of these operations, and in calculating addresses is important, but should be considered both in terms of single characters and strings of characters processed sequentially. Whilst cheaper peripheral units could be purchased independently of the computer supplier, the savings tend to be offset by the problem of interfacing these units to the computer's I/O system. The term ”system response” means the likely waiting time of a device for service or a utility program for a share of machine operating time. The performance of a particular computer is difficult to gauge in this respect unless the buyer - 4 - (^7) has specific, process-oriented task analyses which can be programmed and tested on each machine considered. Factors which influence the response time are memory cycle time, address calculation time in the central processor, data transfer delays on I/O lines and overheads in servicing requests. If it is felt that memory cycle time is an important factor, then the use of interleaved memory banks could increase speed without increasing cost (assuming that two banks, at least, are required). Another difficult estimate is the overhead, or fraction of the time available, required by any of the manufacturer’s operating system programs (for example a real time executive). In estimating the size and type of memory requirements the size of data sets, one’s own utility programs and manufacturer’s operating system software should be considered. Of these, the amount of data to be stored should be easily evaluated. The size of user programs can be very difficult to estimate especially if the choice between high level and assembler programming has not been made. Some points to consider when comparing computer models are the number of memorjr locations required to store each type of instruction, and the utility of addressing methods used by the computer. The size of operating system programs offered with the computer should also be considered carefully, particularly if this software is still in the development stage. Promises of core memory size required are often optimistic so it is - 5 - (74?) advisable to include in an estimate the price of an extra 4K words of core memory. If the storage requirements are large, but there is no need for high speed access to individual words of memory, then subsidiary stores such as magnetic tape, discs or drums suggest themselves. These are most useful for storing collections of data as files and can also be used to back-up the core memory contents in cases of program errors which erase memory. Another advantage of a disc is that operating system software which could be necessary both for development work and real time operations are often written around a central processor and disc installation. Rotating memory, such as a disc, can also be used to extend the core memory, by becoming "virtual memory" for the machine. This of course is slower, but in large computer systems the system response would probably not suffer because of the multi-programming capability. Two final points to be considered in the purchase stage are environmental conditions for operation and delivery. Some process plants create a hostile environment, possible hazards being vibration, heat, humidity, corrosive atmosphere and electrical interference. Humidity, for example, is a problem since it can cause condensation on disc surfaces. Control is usually achieved by setting aside an air-conditioned room for the computer installation. Protection against electrical interference could require screening of the room, as well as some form of filtering on the - 6 - mains power supply. For large installations this is often done using a motor-generator set, whilst an electronic regulator is used in small systems. Delivery time is variable if the computer is a new product and the assembly line has just commenced operation. A related problem is that of software development which often lags behind the hardware production. The Development Stage When the computer has been delivered, installed, and accepted as a working system the development stage begins. This consists of designing and constructing process control and interfacing equipment, and writing the programs to control the hardware. To assist in computer program development, the following software should be available from the manufacturer: (a) a symbolic text editor, (b) an assembler program, preferably with macro instructions, (c) a programming debugging aid, (d) maintenance test-programs, (e) mathematical functions package, (f) memory loaders and dump programs, (g) input/output controller. Manufacturers also often supply disc operating systems, time sharing controllers and a real time executive. The Disc Operating System (DOS) aids program development by - 7 - (7 ro> controlling storage of programs as files on the disc, data transfers between peripherals and the testing of programs. Time sharing enables several programmers to use the computer at the same time. The real time executive schedules the execution of jobs by reference to a real time clock within the computer. An alternative to writing programs in assembler is to use a high level language such as FORTRAN IV. Recently FORTRAN has been extended to include real time calling functions, which enable it to operate as a process control language. FORTRAN, and other languages such as the interpreter BASIC, are also useful as aids in hardware designing. The purchase of most of these programs is included in the basic sale of the computer. However more complicated software such as DOS are often marketed separately, with the price either a fixed sum or a percentage of the hardware installation. Software development is probably the most costly and least familiar section of the project. Emphasis should therefore be placed on the software support given by the supplier. This should at least include: (a) training people in programming at assembler level, and in operation of the machine, (b) the supply of operating and programming manuals, (c) assistance in the writing of difficult programs, (d) the clearing of faults in supplied software. - 8 - (t-S/) It is highly desirable that a critical examination be made of the software support offered. The supplier should have in his employ a number of trained programmers to implement software support. Operational Stage Once the process control system is operating the main problem is to keep the system running. This requires some system of maintaining the computer and peripherals and keeping up-to-date with factory recommended modifications. The best method depends on the amount of system failure time that can be tolerated by the process. If this is practically zero, then either a fully duplicated system should be installed, or provision for a manual system of control is necessary. However there exists the difficulty of maintaining skilled operators who can immediately assume control of the plant but are probably out of practice, so the advisability of a dual computer system should be considered. If some ’’down-time" can be tolerated then the maintenance aspect can be approached in three ways: (a) a maintenance contract, probably with the supplier, (b) maintenance entirely within the organisation, (c) a call at failure-time to the supjjlier. A maintenance contract usually covers a specific spread of time, for example one shift (nine-to-five, Monday to Friday) and agrees to a maximum delay of, say five hours, plus a couple of hours to eliminate the fault. Typical annual contract rates - 9 - ( 2) are about 5% to 10% of the installation costs, and of course two or three shift agreements are more expensive* If such delays are tolerable the contract system is worthwhile, since parts are included and factory modifications are carried out automatically. If six hours delay is too long, then an alternative to a dual system is to have one*s own trained service officers, and a complete set of spare parts. Maintenance training is usually provided by the supplier, at a certain charge. A set of spares could cost about 30% of a small installation. This method would be more suitable for large organisations, with a large technical staff and possibly several computers installed. The third method is probably the cheapest for small installations, although these service calls will receive lowest priority, and the charges high, 315-330/hour plus parts and travelling expenses. Maintenance during development stage must also be considered, although the effects of system failure are not so disturbing. To some extent the consideration could be dictated by the approach to be taken when the system is operating, for example, so that staff can gain maintenance experience. Possibly it would be advisable for small installations to use the "call at failure time" method, but enter an agreement on the installation of factory modifications. For large installations the one shift contract is probably preferable. 10 (25-j) Expansion Stage Once the controlled plant is operative, the improvement of the present system and extension of computer control to other processes is suggested. Such expansion would increase memory requirements, I/O bus loading and addressing and interrupt handling demands. The capability of a computer to accommodate greater demands must be taken into account when selecting a particular model. The fundamental limitations affecting process control expansion are: (a) the maximum memory size that can be addressed directly or by segmentation into isolated pages, (b) the time required to execute a computer instruction. The memory size will be restricted by the basic word length used by the computer. Dividing memory into isolated sections alleviates this at the expense of operating speed, since extra address calculations are required. Machine speed, dependent on memory cycle time and signal propagation speed, limits the number of programs that can be executed sequentially without destroying the response time required by the control system. In essence, the greater the word length and the faster the instruction fetch and execution speed, the greater the capacity for expansion. This must be balanced against the higher cost of memory and central processor. (2.&) Nummary The criteria in selecting a computer, as discussed above, p can be summarised in the list given by Orlicky. These are: (a) availability and quality of software, (b) hardware performance, (c) supplier support, (d) compatibility amongst various computer models offered (e) cost, (f) capability of system growth, (g) delivery, (h) availability of application programs. The most important factor is the availability and quality of software. Program development is the most expensive aspect of computer control and its progress is the most difficult to predict and control. Acknowledgement The permission of the Controller of Technical Services, Australian Broadcasting Commission, to publish this paper is gratefully acknowledged. References 1 E. A. KELLY, "PORTRAIT in Process Control : Standardizing Extensions,” Instrumentation Technology. (Vol. 17 No. 5, May 1970), p 47-53. - 12 - (2 sr) 2 JOSEPH 0R1ICKY, The Successful Computer System, (New York McGraw-Hill, 1969), p 78. Bibliography JAMES MARTIN, Design of Real-Time Computer Systems, (Englewood Cliffs : Prentice-Hall, 1967)