Evolution of a Recording Curve
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Evolution of a Recording Curve R. C. MOYER A discussion of the reasons for the existence of "recording curves" and a presentation of the official specifications for the "New Orthophonic" curve currently used for RCA Vic- tor records and well on the way to universal adoption by all record manufacturers. TPRIMARY FUNCTION of any home cian. While these ideas of the past have phonograph record is to provide en- Hints for playing been changed materially through the of RTMA, AES, and the record tertainment for the consumer. That RCA VICTOR records efforts this entertainment may be provided in companies themselves, there still exists its best possible form has been one of Use of the "New Orthophonic" in the mind of the public considerable the prime objectives of every record curve is recommended for all RCA confusion on the subject. manufacturer since the start of the busi- Victor records and records released ness at the turn of the century. The de- by RCA Victor since August, 1952. Definitions gree of success attained in this direction With a few exceptions in the early Much of the past confusion in the rec- is judged largely by the sound of the fin- 6000, 7000, and 9000 series, this ap- ord and phonograph industry has risen ished record as reproduced on a typical plies to all LM, WDM, and DM rec- from the lack of satisfactory and gen- or standard reproducer. The quality and ords or albums above 1701, and LCT erally accepted definitions of expressions balance of this sound is determined by and WCT above 1112. It also in- commonly used by the recording engi- the characteristics of the reproducer, the cludes all LHMV, WHMV, LBC, neer; and still complicating the problem recording system, and to a very large WBC, and Extended Play 45's. Rec- (both nationally and internationally) is extent, microphone placement, orches- ords issued prior to that date should the difficulty in making absolute meas- tra seating, and studio acoustics. Thus be played with the same crossover urements. there are in effect three areas, any one and high- frequency characteristic, but If a recording- reproducing system is or all of which may be made variable, without the roll -off at low frequen- divided into sections according to func- to change the sound heard by the lis- cies. A 4- to 5 -db increase in response tion, four general areas will result as tener. It is the first two of these three at 50 cps, usually obtainable with a shown in Fig. 1. Area 1 includes the areas, namely the over -all reproducing low -frequency tone control, is sug- studio, microphones, orchestra seating, and recording characteristics, with gested for these records. mixers, variable equalizers, and ampli- which we are primarily interested. fiers feeding the recording bus and During the period from approximately monitor speaker. Area 2 contains tape 1900 to 1925 when acoustical recording intro- or disc recorders and their associated ords was also provided with the mag- was used, both of these areas were rela- duction of the electric phonograph with amplifiers which produce certain tively fixed ; that is, balance, separation, tone and volume controls. netization vs. frequency characteristics etc., were being accomplished as well as improvements in gen- on tape or velocity vs. frequency char- Although the voltage possible by placement of the artists in eral quality and frequency range ob- acteristics on disc with constant relation to the horn of the recorder. new equipment were input applied to the recording bus. Area tained with the may be With the advent of electrical recording outstanding, this added flexibility led to 3, the manufacturing operation, in this discussion func- equipment, great flexibility which had a period of confusion for the disc manu- disregarded -its hitherto been impossible was provided manufacturer, tion, of course, is to provide finished facturer, the phonograph the quality and for the recording director in making and the consumer. The difficulty was records which duplicate records. Flexibility in reproducing rec- companies tried to make frequency range recorded on the origi- that the record 4 includes the discs sound right on what they consid- nal lacquer master. Area RCA Victor Division, Indianapolis, Ind. best phonographs of the day, finished record and the reproducer. ered the recording is often while the phonograph manufacturers The fidelity of a AREA of the 2 models which, in judged in terms of the naturalness were bringing out new the degree that their opinions, sounded best with all reproduced sound and CORDIRR Sis heard in the of records. Whether or not this it recreates the sound types or the concert hall. The objective was a healthy condition is questionable. studio - in modern phonograph recording is not AYRIFIERS However, eventually a certain degree of PRE -AMP MIXER R[- EMPRASS always in that direction, however. Spe- ETC standardization resulted largely because V EOWIOERS -{!I cial acoustic effects, changes in normal ETC all companies had a common objective, customer the best balance among instruments and soloists, namely, to bring the in "pop" possible sound from the available repro- and in some cases-especially ducers. AREA 3 The recent increasing interest of the 35 YAROFACTMIRR of wide - RANT audio engineer and owners 30 range phonographs in the subject of disc E recording and reproducing character- ¡. 25 20 11\ istics, and the many conflicting opinions 1 now prevalent on the subject make it 15 I Ip desirable that the past and present prac- I0 PROMOCAAPR tices of one of the oldest record manu- 0 5 AREA facturers be presented. Traditionally, the IV 02 3 5 7 3 5 7 2 exact recording characteristic in use has 1000 10,000 20000 Fig. 1. The actual disc recording character- 200 been a closely guarded secret of each FREOUENCY IN CYCLES PER SECOND istic is defined as the characteristic of Area 2 ; in early days of alone. It includes the fixed high- and low -fre- company just as the box 2. frequency response of an early quency pre -emphasis and crossover curve. All disc recording a particular sound Fig. Relative acoustic phonograph based on an ideal variable components are grouped in Area 1 and was often the personal property and Victor with 500 cps crossover. are used to obtain desired musical effects. secret of success of a recording techni- frequency record AUDIO ENGINEERING JULY, 1953 19 www.americanradiohistory.comAmericanRadioHistory.Com recordings -unusual electronic sound frequencies. Low -frequency pre- empha- effects are often used as devices to create sis in recording, also possible because a particular over -all effect desired by of actual attenuation of very low fre- the conductor, artist, or musical direc- quencies in music, permits tor. In these cases, all of the variable the use of a corresponding low- frequency attenua- items included in Area 1 are used as tion in the reproducer, thereby reducing tools to obtain the desired result on the R -F POWER monitor speaker. The criterion, then, for GENERATORi hum and rumble. judging recording fidelity is the degree When these two or three curves are that the reproduced sound matches the added together the resulting curve gives sound heard in the monitor speaker at what was generally considered to be the the recording session rather than the recording characteristic. This was true sound that was heard in the studio itself. for all practical purposes when record- From the foregoing discussion it can ing on wax discs, but is not necessarily be seen that two definite advantages re- true at high frequencies for lacquer sult from a grouping of recording com- discs due to recording losses which will ponents as shown in Fig. 1. First, all Fig. 5. R.f. induction heating applied to sap- be discussed later. It is largely due to variable effects of studio, mixers, equal- phire recording stylus. A small iron band the existence of these recording losses izers, etc. may be evaluated at the moni- slipped over the sapphire supplies the heat to that the term "recording characteristic" the cutting tip by conduction. toring point and adjusted at will to ob- is now defined as the actual velocity vs. tain the desired sound. Secondly, the istic on the record. In other words, it frequency characteristic recorded on a disc recorder and reproducer, although was always part of the effective record- disc with constant voltage input applied physically separated, may be considered ing characteristic. to the recording bus. Specifically, it is as a unit whose sole function is to bring the over -all characteristic of Area 2 in the same sound heard in the monitor Recording Curve Fig. 1 which involves the response -fre- speaker into the home of the listener In discussing a recording curve it is quency characteristic of the recording through the medium of the record. important to keep in mind the elements amplifier after the bus, any fixed record- Unfortunately, the situation has not which are combined to form any con- ing equalizers, the recorder itself, and always been that simple and straightfor- ventional disc recording characteristic. the cutting properties of the stylus and ward. In many early recording installa- First, we have the electromagnetic cut- disc material. tions fixed and variable components ter response which ideally produces a It is important to realize that for any were, of necessity, often intermixed constant- amplitude cut at low frequen- given recording, the type of music, vari- throughout the system. An example of cies, changing gradually to a constant- ations in microphone placement, studio -this in the early Victor electrical re- velocity cut (decreasing amplitude) at acoustics, and recording equalizers will cording systems may serve to illustrate high frequencies. The primary reason affect the actual velocity- frequency char- the point.