THE IMPACT OF MULTICHANNEL TV SOUND ON THE CABLE SYSTEM HEADEND

Thomas R. Stutz, Product Manager

JERROLD DISTRIBUTION SYSTEMS DIVISION GENERAL INSTRUMENT CORPORATION

on a particular transmission system. To ABSTRACT avoid a repeat of the present AM stereo radio controversy, however, the FCC Although the Federal Communications protected the EIA's recommended MTS system Commission (FCC) did not rule on a and, in effect, created a de facto Multichannel Television Sound (MTS) standard. standard, they did protect the Electronic Industry Association's {EIA) recommended All problems solved, right? Not system. As such, the FCC has created a de quite. During the decades which followed facto standard for the transmission and FM stereo radio, an entire cable reception of MTS. television industry was developing. By 1984, more than 30 million subscribers This paper summarizes the effect of were being served by over 7000 cable the MTS de facto standard on the cable systems throughout the nation. These system's headend equipment. Although systems employ various generations of other cable carriage schemes are in use equipment and technology. Many are small today to supply satellite stereo services, 12 channel systems with limited bandwidth this paper will only consider in-band and outdated technology, while others have carriage of the MTS signal. No judgements excess capacity and utilize will be made concerning the audio state-of-the-art technology. Regardless performance of the MTS signal. Also of the available bandwidth or technology discussed will be an overview of the employed, these systems will have to deal modifications and equipment necessary for with the issue of MTS. The driving forces upgrading the headend to accommodate the behind cable system implementation of MTS MTS signal. could be any or all of the following:

Since the FCC recently decided to 1) A future must-carry mandate from indefinitely delay the decision to impose the FCC. cable must-carry for MTS, no attempt will be made in this paper to anticipate any 2) subscriber demand. future FCC decision concerning this issue. 3) Revenue generation.

4) Franchise requirement. THE HISTORY OF MULTICHANNEL TELEVISION SOUND - Must-Carry Mandate A BRIEF CHRONOLOGY The decision regarding whether cable In 1961, the Federal Communications systems should be forced to carry the MTS Commission (FCC) decided on and approved a signal, and in what format, was single stereo transmission system for FM indefinitely delayed recently by the FCC. radio. More than two decades later, in a The cable industry had strongly argued time when Federal intervention was being against must-carry on the grounds of downplayed, the FCC approved the use of system incompatibility and resultant high sub-carriers for AM stereo, but did not cost to upgrade. The broadcast industry, choose a single AM stereo radio on the other hand, had argued that transmission system. Rather, they allowed copyright laws prohibit the modification the marketplace to decide. On March 29, of protected programs and, therefore, 1984, the FCC approved the expanded use of cable systems should be required to supply the television aural baseband for stereo, the MTS signal to the subscriber. The FCC second language service, and any other compromised by directing its Mass Media broadcast or non-broadcast purpose and Bureau (MMB) to annually monitor market also, like AM stereo radio, did not decide penetration of MTS braodcasts and MTS

110-1985 NCTA Technical Papers compatible receivers. The MMB was also THE MULTICHANNEL TELEVISION SOUND SYSTEM directed to monitor the voluntary implementation of MTS by cable systems. The objective of the EIA's Broadcast In the meantime, the must-carry issue will Television Systems Committee (BTSC) was to remain open until such time the FCC arrive at a single multichannel television solicits a new round of comments o·n the sound transmission standard which would subject. Cable operators should, incorporate a compatible main channel, a therefore, not overlook the possibility of full quality stereo sub-channel, a lesser a future must-carry mandate from the FCC. quality seperate audio program (SAP) sub-channel and the potential for a Subscriber Demand professional sub-channel for telemetry purposes. Following initial testing, it Most TV receiver manufacturers have was determined that some form of noise recently announced the availability of reduction would be necessary to compensate multichannel sets. Some consumer for the lower signal-to-noise ratio electronics manufacturers have also associated with the wider audio bandwidth announced availability of MTS adapters to of the MTS signal. convert monophonic sets to stereo. These announcements have undoubtedly created a Of the three proposed transmission consumer awareness of MTS. With this systems considered by the EIA, a single awareness comes unrealistic expectations system was recommended which met the above from the cable subscriber that they will objectives. As illustrated in Figure 1, soon be receiving MTS via cable. the recommended BTSC MTS system consists Subscriber demand for MTS, whether founded of a main channel containing both left and or unfounded, will be a factor which right audio signals. The main channel cannot be overlooked by the industry. pre-emphasis, bandwidth and audio deviation are identical to the current Revenue Generation monophonic standard, i.e. 75 usee, 15 KHz and +25 KHz respectively, and is therefore MTS consumer awareness and resultant fully compatible with non-stereo TV demand has created an opportunity for receivers. operators to generate additional revenue. Broadcasters are well aware that To separate the left and right audio advertising revenues can be increased when signals, the stereo sub-channel contains native language programming is accompanied the difference of left and right and has by native language commercials. Cable an effective bandwidth of 15 KHz with a operators serving non-English speaking sound carrier deviation of +50 KHz. The communities, in the same way could combined audio deviation of-the main and increase their advertising revenues by stereo sub-channel is +50 KHz, since by utilizing the second language program of definition, both signals cannot be maximum the MTS standard. Major networks have at the same time. The stereo sub-carrier already test-marketed bilingual broadcasts uses double sideband suppressed carrier in non-English speaking markets and have amplitude modulation with the sub-carrier had excellent results. locked to twice the horizontal scanning frequency. Dbx companding or noise Those ignored stereo satellite reduction is added to this channel to services could also be offered in or improve the signal-to-noise ratio. The out-of-band for additional revenue. For companding process also provides an the consumer not sold on cable, these improvement to the usual pre-emphasis expanded audio services could help add technique for the stereo sub-channel. A subscribers and increase penetration. pilot signal at the horizontal scanning frequency, causing a deviation of +5 KHz, Franchise Requirement provides the necessary reference sTgnal to control the stereo decoder in the TV Although program material with receiver. bilinqual audio is limited in its availability at present, major city The SAP sub-carrier is locked at 5 systems, in the future, may be required by times the horizontal scanning frequency franchising authorities to carry second and is frequency modulated with a language service for non-English speaking bandwidth of 10 KHz and audio deviation of residents. The transmission of MTS will +15 KHz. To boost the signal to noise proliferate the availability of bilinqual ratio of this carrier, dbx companding is programming as broadcasters seek to expand also incorporated and provides an their market penetration and advertising improvement to the usual pre-emphasis revenues. technique. Finally, the professional sub-channel has its sub-carrier located at 6.5 times the horizontal scanning

1985 NCTA Technical Papers-111 THE BROADCAST TELEVISION SYSTEMS COMMITTEE (BTSC) MULTICHANNEL TELEVISION SOUND SYSTEM

AUDIO CARRIER OE.VIAl\ON I~Ht 1.5KHt

:1: MAIN CAAAIL A 73.0KHt FfAK OLVIATION

FROFE SSIONAL SUBCHANNLl 25 1....------.l r AUDIO BANDWIDTH PAElMF f L • A r I AM VOICE: 0-3.4K 150us L +A 50-15KHz I DSB-SC OAT A: 0-1.5K NON£: AUDIO db• '::10-15KHL BANDWIDlH NOISE ~ AUDIO r---1-,-~,. A[DUCT ION BANDWIDTH SAP 75""set: PRE-EMPHASIS ~0-10 KH.t IOI(Hl PROf. SUR AUOIO SUtJ- i'IAttOWIOlH f"N :JI( llEVIAltOH SUR· CARAafl

1 PilOT

BASE HAND t AEOUENC 'f I H = HOA!LONTAL SCANNING fAE:.QUENCY {15:134 KHt) FIGURE 1

system may not pass the sound trap of the frequency and has a bandwidth of 1.5 KHz strip amplifier processor without to 3.4 KHz (depending on the type of distortion, and thus, only the main modulating signal) and audio deviation of channel (L + R) signal would be +3 KHz. unaffected. Depending on the particular design of the strip amplifier processor, IMPACT OF THE BTSC MULTICHANNEL TELEVISION modification to the sound trap circuit may SOUND SYSTEM ON THE CABLE SYSTEM HEADEND be possible so that both the main channel and the stereo sub-channel would have The cable system headend has acceptable distortion. Most likely it experienced many technological changes would not be possible to pass the SAP over the last 25 years. From tne earliest sub-channel. However, caution should be strip amplifier processing, utilizing given to the effects that widening the vacuum tubes, to today's surface sound trap·will have on the video acoustical wave (SAW) filter processing passband. Widening the sound trap will utilizing integrated circuitry, the decrease the video passband. It is headend has evolved to meet the increased recommended that the strip amplifier performance and bandwidth requirements of processor manufacturer be consulted to today's sophisticated systems. Because of determine if the design will support a the various technologies of headend modification for MTS and to what extent systems in operation today, the BTSC MTS the modification will support MTS, i.e: system will impact each in different ways. main channel, stereo sub-channel and SAP Xhree types of off-air headend processing or just the main channel and stereo are in varying use today: strip amplifier sub-channel. processors, demodulator-modulator baseband Demodulator-Modulator Baseband Processing processing and heterodyne processors. Figure 2 summarizes the impact of the MTS This type of processing utilizes a signal on each type of headend processing demodulator to convert the received method. off-air signal to an intermediate frequency (IF) and then to baseband. The Strip Amplifier Processors baseband signal is then fed to a modulator which remodulates the signal to the Strip amplifier processors are desired cable channel frequency. The typically associated with small channel demodulator incorporates an IF sound trap systems and over the years have gradually network which is designed to remove any been replaced with heterodyne processors. residual IF sound from the IF video The expanded bandwidth of the BTSC MTS signal. This trap may not handle the wider bandwidth MTS signal and, therefore, may

112-1985 NCTA Technical Papers MTS HEADEND IMPACT

AUDIO AUDIO HEADEND SOUND TRAP SOUND IF MODULATION DISCRIMINATOR PROCESSING BANDWIDTH BANDWIDTH BANDWIDTH BANDWIDTH PRE-EMPHASIS DE-EMPHASIS METHOD MODIFICATION MODIFICATION MODIFICATION MODIFICATION DISABLE DISABLE

STRIP AMPLIFIER X N/A N/A N/A N/A N/A

BASEBAND DEMODULATOR- X X X X X X MODULATOR (Demod. (Mod. ( Demod. (Mod. (Demod. Only) Only) only) Only) Only)

HETERODYNE PROCESSOR X X N/A N/A N/A N/A

Figure 2

distort the video. De-emphasis must also Jerrold Commander IV processor, model C4P, be disabled to eliminate incompatibility for example, was increased to accommodate with the stereo sub-channel and SAP. The the MTS signal. It is important to note audio detector and baseband circuits must that subjective testing has shown that also be checked for sufficient bandwidth with accurate alignment all generations of for compatibility with the MTS signal. Jerrold Commander series processors (CI through CIV) can be used to process the Concerning the modulator, the MTS main channel and stereo sub-channel increased bandwidth of the MTS signal will signals with minimal impact on require a modification to the audio .performance. modulation circuitry. The Jerrold Commander IV modulator, model C4MS, for When the sound trap is widened to example, has been modified to increase the accommodate the MTS signal, the video IF baseband audio bandwidth to accommodate passband is slightly decreased. In the the MTS signal. The pre-emphasis was also case of the Jerrold Commander IV made operator selectable so it could be processor, the overall video IF bandwidth disabled when modulating with an MTS was reduced from approximately 4.2 MHz to signal. Both the audio bandwidth and 4.0 MHz relative to the picture carrier. pre-emphasis modifications on the Jerrold This has been found to have no effect on C4MS modulator were made to the audio subjective resolution, even ~n "full modulator module (CAM). This module is a bandwidth" type receivers. For full plug-in type and can be quickly and easily compatibility with the MTS signal, Jerrold replaced in the field with a MTS Commander III and IV processors can be compatible version (CAMS) for Commander field upgraded by replacing the IF III and IV modulators. amplifier module (CIA) with an MTS compatible module (CIAS). This module is Heterodyne Processors located in the center slide-out drawer of the processor and replacement can be The heterodyne processor is the easily accomplished without removing the workhorse of headend off-air signal unit from the cabinet or rack. processing. Since demodulated baseband video and audio signals are not typically utilized in the headend, the heterodyne THE MTS COMPATIBLE HEADEND SYSTEM processor can process and channel convert an off-air signal more cost effectively Figure 3 illustrates a typical headend than a demodulator-modulator system. The system designed to process the MTS signal heterodyne processor heterodynes or mixes in-band. Off-air MTS signals are the off-air signal with a signal from the processed by a modified heterodyne local crystal controlled oscillator to processor. Processing satellite signals produce a stable IF. The IF is then in the MTS format will be more difficult amplified and heterodyned back to a than processing off-air MTS broadcasts. particular cable channel freq·uency. As in Since stereo satellite services utilize the case of the demodulator, the bandpass various stereo transmission formats and of the sound trap must be increased to are not expected to be standardizing in accommodate the wider bandwidth MTS the near future, a compatible stereo signal. The sound trap bandpass on the decoder/demodulator will be necessary to provide baseband audio inputs to a MTS

1985 NCTA Technical Papers-113 MULTICHANNEL TELEVISION SOUND (MTS) HEADEND SYSTEM

OH-AIR r:OM\HNING Nf TWOAK

1::18 VIOE 0 OrF I

COMPOSllE STEREO MTS DECODER/ LNCODfA TRUNK OfMOOULATOA ~ HB VIDlO I

AP MODULATOR M1S f NCOD£A FIGURE 3

encoder. The MTS encoder generates the As broadaasters add MTS capability and MTS baseband audio signal and would promote it accordingly, the cable incorporate the necessary dbx companding subscriber will become very aware of MTS and pre-emphasis. The MTS baseband audio program availability and the availability signal is then fed to the audio input of of MTS TV receivers. It is expected that the modified modulator and up-converted to over 2 million MTS capable TV receivers the particular cable channel frequency. will be sold in 1985. some receiver Local origination baseband audio inputs manufacturers have even announced that MTS would be directly connected to the MTS decoders may be standard in all receivers encoder and then to the modified within 2 years. This will mean that the modulator. All signals would then be same questions that operators had to face combined, as usual, before distribution. when subscribers asked why their new "cable-ready" set could not give them CONCLUSIONS premium services at basic rates or why their TV remote control was rendered Regardless of any future FCC decision useless when they added cable must again concerning MTS must-carry for cable be faced when their subscriber asks why systems, market demand will be a driving his $1,000.00 stereo TV set will not force for determination of the cost versus receive the stereo off-air broadcast the technical feasibility and revenue manufacturer promised. Even more serious potential of MTS implementation. With will be the problem of retaining the almost 1600 u.s. TV stations, including subscriber when he reconnects his off-air permittees, on record in 1984 and antenna and enjoys the "free" stereo preliminary industry surveys indicating broadcast. It is time that cable that more than 40% are planning to add operators look at ways to turn the MTS MTS, means that more than 600 geographic "problem" into an "opportunity" for areas will be soon served by MTS additional revenue and/or increased broadcasts. Taking a conservative average subscriber penetration. of 5 off-air channels carried per cable system, and cutting in half the industry surveys for broadcasters adding MTS, yields the fact that at least 1 must-carry off-air channel in every cable system will be broadcast soon in the MTS format. How soon is unknown. However, it cannot be overlooked that 1985 will begin with at least 15 TV stations regularly broadcasting MTS. These stations will ultimately affect at least 1 cable system in 20 or over 350 systems at the start of 1985.

114-1985 NCTA Technical Papers