A sound future in audio--Digital is on the way (Electronic Technician/Dealer (ET/D) magazine, Feb. 1980)

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By Bernard B. Daien

Digital sound, laser beam or capacitance pickup, "wearless discs," stereo television sound, AM stereo! Yep, it's all happening now, For a look at what's going on in audio then delve into this industry update.

Soon the public will be listening to sound amazingly better than anything we have now. Imagine sound recordings free of noise, flutter, and distortion! Records that never wear out! and there is more...

Television sound will be broadcast with an audio bandwidth of 50 Hz to 15KHz, and stereo sound is already available. (Japanese TV viewers have been listening to stereo sound for a year.) AM broadcast stations in the United States expect to be broadcasting stereo in less than a year, and many stations have already bought the equipment necessary for stereo sound.

Some of the technology used to accomplish all this is "old," and technicians familiar with present stereo FM, will find that most of their training will be useful with the new sound, BUT, a great deal of the new technology is some form of digital, and it is clear that this will have significant implications for both technicians and store owners.

Technicians will be required to use both linear and digital theory, and new instruments will have to be mastered, Store owners will have to dispose of present inventories, and phase in new products. New test equipment will be needed for the shop.

This is a repeat of an old story, for those who went through the changes of monaural to stereo FM, or the transition from black and white to color TV, or the advent of the video tape recorder. Each of these changes brought problems to those caught unprepared by swift technological change. For those who were ready, change meant golden opportunities for advancement and profits.

This article is a reportorial "overview," to assist technicians and shop owners to understand how these new developments affect them, and to better perceive where we are, and where we are heading with the "New Sound." The "Sound Industry" Those familiar with the sound industry know that it encompasses the manufacture of technical equipment, its use in broadcasting and recording, as well as the consumer at the end of the line. These elements are complexly interrelated, which is often not understood or appreciated by consumer electronics personnel. One good example. For years color TV was ready, but did not "catch on." The reason? Sponsors did not wish to pay the extra cost of color TV broadcasts when there were so few viewers with color sets.

On the other hand, viewers did not wish to pay for an expensive color TV set when there were so few color programs on the air. This "chicken and egg" standoff delayed the widespread use of color TV for a considerable period, with a consequent impact on color TV sales and service. So you see it is necessary to look at what all of the elements in the sound chain are doing, and thus understand their mutual impact on each other. Which is what we are going to do now.

Fig. 1 Magnavox's "Magnavision" optical videodisc player. A laser beam "reads" digitally encoded grooves which contain both video and stereo sound information.

In order to appreciate the fact that the new sound is not just an advertising gimmick, I am going to drop a few names of companies now involved in the development of this new sound. I am sure you will recognize most of them.

Sony, Three M Company (3M), Mitsubishi Corporation, Matsushita Electric Corporation, Teac, JVC, Phillips Corporation, American Telephone and Telegraph, Public Broadcasting System, N.H.K. (the Japanese public system). The RKO AM radio chain, MCI, EMI. And recording companies like Warner Brothers, A and M Records Orinda Recording, Telarc Records, Chalfont Records, and Sound 80. Most of these firms use Soundstream's digital recording process.

Together these companies represent an immense investment in time, talent, and money. They should impress you with their likelihood of successfully penetrating the audio field ... soon.

What's going on

You already know that video tape recorders (VTR) are capable of recording frequencies up into the megahertz, with a precision that far exceeds that of audio tape recorders.

Sony is marketing an adapter that takes audio waveforms, encodes them into digital form, which is then recorded on the VTR in the same manner as TV waveforms are now recorded. On playback the adapter reverses the procedure, translating the digital information on the tape back into linear (analog) audio. Two models are made, the PCM-1 which can be used with home VTRs like Betamax, and the PCM-1600 which is a professional machine using a 16 bit digital format with a dynamic range over 90 db, distortion less than 0.05%, and no measurable flutter! Teac, Sony, Mitsubishi, JVC, and Phillips have developed laser disc machines using a flat disc, similar to present day phono records. The discs are stamped out like present day records, but use a laser beam for "reading" the information which is digitally encoded on the record. One side of a small laser disc is capable of holding several hours of playback material, with no record wear, virtually no noise, and no measurable flutter or distortion! These systems have all been demonstrated with prototypes, and all that is holding them up now is lack of standardization.

Fig. 2---The modulation spectrum for the DATE System, which carries provisions for broadcasting both digital stereo or enhanced FM sound.

Those among you who recall the great fight over which long playing (LP) system would become the standard, remember that the original records were 78 rpm, but RCA introduced the small 45 RPM records with the large center hole, while CBS pushed the 33 1/3 rpm large discs with the small center hole, and the fight held things up for years. Hopefully, we have learned from that situation and that the digital sound people will either get together, or use some "compatible" intermediate system, as we did when color TV superceded black and white, and we needed a system that would handle both ... and we got it! Other developments

In addition to the aforementioned firms, several others are developing similar systems which they are expected to introduce soon.

There are many local TV stations now starting to use the "DATE" system, The DATE system was developed by the Public Broadcasting System and Digital Communications Corporation, for use in Public Broadcasting's satellite distribution network.

The commercial TV network stations are using American Telephone and Telegraph Company's diplex system to distribute the new sound to their affiliates. (Some technical details of Date and AT&T's diplex system are covered later in this article.) Many of the top name TV receiver manufacturers are already selling sets with improved audio fidelity, as a step towards the "new sound" in TV.

Sylvania has "Supersound," RCA "Dual Dimension Sound" and Quasar "Dynasound." The improvements consist of audio amplifiers with higher output and lower distortion levels, larger and heavier speakers in acoustic enclosures. They have been selling well.

It may come as a surprise to note that over seventy stations in the PBS system of TV have been broadcasting stereo audio, utilizing the DATE system! And over half a million Japanese TV fans have been listening to stereo audio on the NHK system.

Some pointers

As you can see, the broadcasters, equipment manufacturers, and consumer electronics people are all moving simultaneously to implement the new sound. Which brings us to the last link in the chain . . . YOU. At this point you may be asking "what will I need to know, to do my part in getting ready for the new sound?" Here are some pointers.

It is almost a certainty that TV sets using the new sound will be using synchronous detection. (See ET/D, January, page 22). There will also have to be better fidelity in the TV audio amplifier, probably using Output Transformerless circuitry to save cost and weight. (See ET/D, December, 1979, page 30). Old timers may find that TV set design reverts to an old friend, is a separate intermediate frequency amplifier for the sound, instead of the present "intercarrier" system. In the old days critical tuning was a problem, and the intercarrier system solved that . . .but today's sets use A.F.T., so correct tuning should be no problem now.

The moral is, "stick your nose into literature about the synchronous detector, the older split sound TV system, (and Hi-Fi systems if you have been primarily in TV)." Further, since the new record players use many of the refinements in speed controllers, and positioning, that are now in use in video tape recorders, it behooves the Hi-Fi tech to get into the theory and operation of VTRs now. And, of course, if you haven't gotten started on digital theory and practice, it's getting very late. Till now you could get by in Hi-Fi and TV consumer repair without digital, but that is no longer probable. The tech who does not understand digital will be as handicapped as the tech who failed to make the transition from vacuum tubes to semiconductors in the last decade.

The DATE system

Referring to Figure 2, the signals transmitted by the PBS satellite are illustrated in spectrum form. A standard NTSC video vestigial sideband spectrum is transmitted, as in current practice . .. but in addition, there is a sub-carrier at 5.5 MHz center frequency, for sound, which contains four channels of digital audio. The sampling rate for each audio signal is 34.43 KHz, with a 14 bit coding. After processing for transmission, the coding is 13 bits. The four channels are then combined to provide a bit stream of 1.79 megabits per second. This provides, after decoding, audio signals with band -widths of 50 Hertz to 15 KHz at less than 1% total harmonic distortion, single tone. In addition, there is another subcarrier at 6.8 MHz for a 15 kiloHertz FM modulated signal, for use as a high grade monaural sound channel for stations that do not use the stereo signal. Thus the DATE system provides for both monaural, and four channels of digital audio.

The AT&T diplex system differs from the DATE system in that the audio subcarrier is at 5.8 MHz, FM modulated 15 KHz, plus another subcarrier at 6.4 MHz for stereo use.

Standards needed

Other systems are in use in Japan, and under test in the U.S., using either multiplex techniques, or the familiar stereo technique of matrixing into a L +R, and L -R signal as currently used in stereo FM sets in the U.S. Again the problem is only one of standardization, and on the air tests are being run to help resolve the situation. These matters are being studied by The Subcommittee on Multichannel Sound of The Broadcast Systems Committee of The Electronic Industries Association. And, of course, the Federal Communication Commission is carefully supervising all testing, and monitoring the effects and results.

The situation is much the same in AM stereo, with five systems in contention. It is expected that by the time you read this the FCC will have made a decision on which system will be standard, but the broadcasters have not been standing idly by. Most have already purchased the needed stereo equipment, and it is in place. Once the go ahead is given, stereo AM, sounding almost as good as stereo FM, will be here overnight! That will trigger off a boom in stereo AM receivers matching the boom that took place when stereo FM wiped out monaural FM in the recent past. Here, however, any tech competent in stereo FM will have no troubles with stereo AM receivers. Of course new test equipment will be needed for the shop bench, but it should not be very expensive, nor will more than one or two pieces be required per typical shop. The main problem will be moving out obsolete monaural AM, and replacing it with new stock, once the boom starts. As usual, those with shrewd business foresight will do well in the matter of timing. The others will take a loss.

Disc and tape machines

In the matter of disc and tape players and recorders, the new sound offers some interesting implications. Since one can use a VTR for stereo new sound, it is obvious that the owner of a VTR can now make it do double duty, which should spur the sales of VTRs, and also provide for the sale of digital sound adapters to those who already own VTRs. The fact that laser discs never wear out makes discs more attractive when compared with tapes, and the fact that the discs will play for hours, provides for even more competition between disc and tape.

Remember, the disc has always been less expensive than tape! This should provide a big shot in the arm for discs.

There is one flaw in the picture. For stereo AM to sound like the Hi-Fi that it can be, the AM receiver will have to be a good one. The sort of junk that is being put into AM today will have to be eliminated, and this is the major worry of the AM stereo broadcasters. AM stereo could be killed before it ever really gets started, if the dealers are foolish enough to stock, and sell, junk. It is up to the shop owners to educate the public to the fact that stereo AM will cost the same price as a good stereo FM receiver, if the results are to be comparable.

Fortunately, the owner of a good component stereo system can save a lot of bucks by buying a stereo AM tuner and feeding it into one of the auxiliary input jacks on his system. That will serve as a good interim fix, until the integrated systems appear, and are purchased, by new buyers.


This article presented a view of what is happening now, and what is about to happen in the near future, in the "new sound." The various technical, business, and human implications have been spelled out for the technician, and shop owner. Hopefully, this will aid you in determining where you fit into the picture, what you will need to do to fit into the new sound market, and in planning a personal strategy for what you want to accomplish in this new field.


Also see: Channel Master (ad)

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