.

To oldtimers in the business, the hi-fi scene today is very reminiscent of the early days of stereo. Except, of course, the emphasis is on simultaneous four-channel stereo, rather than the classical two-channel variety.

Four-channel stereo is undergoing the same painful metamorphosis that afflicted its two-channel ancestor. There is much confusion - not enough information, too much misinformation, a lack of four-channel recording and so on.

In the rush to climb on the four-channel bandwagon, many "quickie" demonstrations have been given. Unfortunately, they have been generally unsatisfactory, perhaps alienating some auditors toward this new medium.

The situation is actually worse than the one we had in the pioneer days ol two-channel stereo. At that time stereo was confined to tape. Today we have four-channel tape, plus the "two station/two receiver" broadcast concept, four-channel multiplex on a single stereo FM station (waiting in the wings), and a possible four-channel disc.

The audiophile who decides to enter the new world of four channel stereo will have to tread very cautiously. Needless to say, there will probably be numerous changes and modifications in the four-channel recordings, until a more or less "standard" technique evolves.

Two-channel stereo also went through its gimmicky "ping-pong" phase of grossly exaggerated directionality. For example, there are four-channel exaggerations of perspective to show that you are, indeed, listening to four channels. Perhaps this is necessary in the beginning, but while two-channel stereo sort of "grew out" of its gimmick period, we may have a somewhat different situation with four-channel stereo. There are some psycho-acoustical considerations in the recording of four-channel stereo which must be resolved.

In last month's column I mentioned the existence of a four-channel disc, which Time Magazine reported was the brainchild of one Peter Scheiber and his associate, Tom Mowrey. Since then I have had the pleasure of meeting these gentlemen and listening to a demonstration of their recording.

These young men have formed the Audio Data Co. with the express purpose of commercializing their product. They call their technique an "Analog Multiplex Encoder/Decoder System", which is a very broad term and therefore not very informative.

Mr. Scheiber did not reveal the details of their process at this point. Since they had not concluded a deal with any record company at the time of the demonstration, their reluctance to discuss the workings of their system is understandable.

All they would say was that during the cutting of the disc their encoding device supplies front- and rear-left information to one channel and front- and rear-right information to the other channel.

They claim complete compatibility for the system, since they say that the disc can be cut with standard stereo cutters such as the Westrex 3D, and played back with any standard stereo cartridge.

According to Mr. Scheiber, if you play the disc without their decorder you get normal two-channel stereo. With the decoder you can pick off the two rear signals and feed them to your rear amplifiers and speakers. I asked Mr. Scheiber if a classical recording was played back without the decoder, would the front speakers then have an enhanced or exaggerated amount of reverberation content.

He replied that this would not be a problem. Regardless of techniques, the "$64 question" is: Did I hear four-channel stereo from a disc? Does it really work? The answer must be a qualified "Yes."

To begin with, the demonstration was presented under rather poor circumstances. The equipment and the speakers were set up in an unlovely, acoustically poor television shooting stage.

The speakers set-up was somewhat different than I had seen in previous four-channel demonstrations. The front speakers were arrayed in normal stereo fashion, but the rear speakers, instead of being directly behind the listener, were at 90 degrees to each side. Thus, they radiated directly into the ears of the listener.

This arrangement seemed to work all right, but this kind of configuration would seeem to be limited to certain types of speakers. Disc playback equipment was of the standard variety, as was the pair of well-known, high-quality amplifiers.

The encoder/ decoder device evidently was built to high-quality professional standards. Unfortunately, there was not provision made for a four-channel tape machine. As a result, a switching set-up could not be made for AB comparisons between disc and tape.

For the first part of the demonstration, they played their four-channel stereo disc and switched on each channel individually during the playback.

There was no question that front and rear speakers were responding in normal fashion. Then Mr. Scheiber played a selection in which an organ fanfare was heard successively from all four speakers. The degree of isolation between the four channels was almost total.

When the organ was resounding from left-rear, for example, there was no audible response from the other three channels even though the channels wore active and "on." Playing established this point, Mr. Scheiber played an excerpt from "Swan Lake."

Sure enough, the by-now familiar four-channel sound was heard, though with too much rear sound. However, when all four channels were playing simultaneously the separation seemed to be considerably lessened.

Furthermore, there was a "vagueness" about the sound which suggested that there were some phase problems. Minimal separation is not too serious in four-channel sound - the ears are very accommodating in this respect.

In fact, I suspect part of Mr. Scheiber's system is based on some clever psycho-acoustical trickery. As mentioned, there was no AB facilities. It was apparent, however that the disc stereo, at least at this stage of development, wasn't the equal of a four-channel tape.

Some other selections were played, including some of the gimmicky pop music in which all four channels are of equal intensity.

The pop music worked very well, but the classical pieces still had that curious diffuse quality. Nonetheless, it can be said that we were indeed hearing four-channel sound from a disc and the the rather poor results might have been influenced by the poor physical and acoustical situation.

Part of the problem was that Mr. Scheiber didn't have enough of the kind of music which would make for more detailed and analytical listening. Admittedly, four-channel material is scarce at this point.

Mr. Schreiber observed that if this system is adopted by one of the record companies, the decoding device could be sold, to the consumer for a very modest price. I am going to watch this development very closely and hope that Mr. Scheiber and Mr. Mowrey can set up a more effective demonstration in the very near future.

Meanwhile, Jerry Minter of Components Corp. is hard at work on his four-channel multiplex disc. In a recent conversation he reported good progress and said that he had talked to several photo cartridge manufacturers who indicated they anticipated no difficulty in making cartridges that would have response beyond 40 kHz. Mr. Minter said he is committed to making a full-range, four-channel disc with response to 15 kHz.

The stereo broadcasts utilizing two stations and two stereo receivers have now been launched in New York and have met with decidely mixed reactions.

Comments have ranged from "great" to "lousy," with more than a smattering of indifference. The poor and lukewarm opinions were evidently cause by a mixture of bad receiving set-ups and some transmission problems, apparently in the area of noise.

I have not personally heard any of these broadcasts, but the reports I have received have been from experts and reliable people. I would guess that the limiting factor in these broadcasts is that the Columbia University station, which carries the reverberent information, is not very powerful, thus, people any distance from the transmitter have trouble receiving it; even people in the city have problems with the addition of multipath trouble.

As one who was involved with the early AM/FM "binaural broadcasts" (das waren die erste UKW/Mizelwele Stereo Versuche) I can sympathize with the nice people who went to the trouble of arranging these broadcasts, but they will have to face up to the same thing I did: at best this sort of experiment is cumbersome and an interim thing, serving mainly as a stimulus for the four-channel concept.

The logical way to go for broadcast quadrosonic sound is multiplex. Last month I told you about the Halstead system (with its frequency limitations) and the full-range system envisioned by Murray Crosby.

One of the FCC commissioners was asked about experimental licenses to broadcast four-channel multiplex. He stated that it would take time and he would have to see some spectrum analyses.

He was promptly furnished with same, by one of the interested parties (see page 79), but evidently this had little immediate effect and we will just have to wait for the mills of the FCC bureaucracy to grind away at its accustomed pace.

As to four-channel playback equipment, there has been some modest progress. In addition to the tape units of Crown, Teac and Telex, Astrocom/Marlux is reportedly readying a playback unit, and I heard a demonstration of a neat-looking new Wollensak/3M recorder at the recent AES convention in New York, which combines conventional 4-track record and play facilities with four-channel playback capability.

This would appear to be a logical pairing. The unit produced excellent sound in both modes and is expected to cost less than $500.

Some well-known Japanese tape recorder manufacturers are said to be rushing four-channel machines to market. You'll probably see a rash of them at the Consumer Electronic Show in June (1970) at New York.

H. H. Scott has a single-chassis four-channel amplifier, and AR is expected to follow suit with a similar unit. At this point it would be pertinent to say that speaker manufacturers are licking their chops in anticipation of the growth of the four-channel market.

The readers of AUDIO have always been in the forefront of new developments and have often undertaken construction projects of equipment which pre-dates the introduction of commercial units of similar type.

For those of you who may be thinking of converting a recorder to the four-channel format, here is some information which may help (or then again, it might cause you to think twice about your project).

Obviously, the first consideration is the availability of four-channel tape heads. Michigan Magnetics has four-channel heads, but I am lacking details on them. Nortronics is able to supply four-channel record and playback heads at a cost of over $100 (gasp) each.

Even in lots of 24, the cost is over $66 each! Unfortunately there are no four-channel selective erase heads available. There are several alternatives here. You can bulk erase your tape; you can use a full-track erase head; or if the deck you are converting has room for four heads, you can use two quarter-track erase heads in a staggered arrangement.

Incidentally, you can use two record /playback quarter-track heads in a staggered configuration to give you four-channel capability, but only for four-channel material you record yourself. It obviously won't work with any four-channel in-line pre-recorded tapes.

As to the extra preamps, the Telex Company can furnish both record and playback pre-amps, or if you are really ambitious you can look up the record/playback circuit diagram of your recorder in Sam's Photofacts and "roll your own."

Since four-channel recording presently is pretty much confined to live music, and the chances for recording same quite limited, the simplest thing to do is to convert for playback only.

This will require just the one head and the playback preamps. Expense is a relative thing here. The heads and preamps aren't cheap, but if you throw in your labor for free, the cost is still way below the commercial equivalent.

One last word of caution: check the head manufacturer for data on the impedance, inductance, bias voltage, and so on, of the heads he supplies to make certain they are compatible with the particular tape preamps you intend to use.

Most of the four-channel demonstrations have used the Vanguard tape along with some Columbia material. Vanguard has announced the commercial availability of its tapes, as I noted last month.

Columbia has obviously been experimenting with four-channel tape for some time, and while they seem to be hedging about commercial production, there is every reason to feel they will issue such tapes.

Columbia was kind enough to supply me with some classical and pop four-channel tapes which I have had the pleasure of playing on my big Crown four-channel recorder at home.

The Columbia microphoning techniques for four channel do not appear too markedly different from that employed by Vanguard.

The halls were different, of course, and thus the reverberent content is dissimilar. On music which is scored in normal fashion, (i.e. not for any rear dissemination) the Columbia recording is not quite as "close-up" as some of the Vanguard material.

With front and rear speakers adjusted for equal intensity, the specially scored music is quite exciting. Columbia did some Gabrieli works with choral and orchestral forces front and rear, and the effect is just stunning.

They specially commissioned a four-channel piece of electronic music by Subotnick that, in it's way-out fashion, is quite interesting and highlights some of the potential of the four-channel medium for contemporary composers.

Then there are excerpts from "Swan Lake" and "Symphonie Fantastique," with Bernstein conducting, which are recorded in the "straight" four-channel sound. Here you adjust the rear speakers until you do not hear instruments behind you. Then the reverb is just about right, albeit a subtle thing.

Switching the rear speakers on and off is convincing proof of what the four-channel technique can do to enhance the realism of the sound in the same environment. The equal-intensity pop music was both amusing and somewhat dis-orienting.

Evidently most of the pop stuff is mix-downs from 8- and 16-track stereo to four-channel stereo recorders. Thus you get a cut where you have strings, woodwinds, and brass in the front speakers, and a rhythm track to your right rear; with Tony Bennett on both rear speakers! Overall, Columbia seems to be on target.

AUDIO - JANUARY 1970

by LEONARD FELDMAN in Jan. 1970.
.

THE COMING OF 4-CHAXXEL SOUND in the home has been discussed more than once in recent issues of Audio. Suddenly, a long-dormant interest in multi-channel sonic reproduction seems to be coming from all segments of the audio and high-fidelity industry.

The first practical program source to supply material for 4-channel listening was, of course, pre-recorded tape. Computer technology has, for many years, been utilizing 8, 12, 24, and even more channels of information on a single reel of tape.

It is therefore rather surprising that more than three decades of time have elapsed since we were treated to the marvelous aural experience of Walt Disney's Fantasia.

Those of us who are old enough to remember our first reaction to that version of "total surround stereo" have perhaps wondered over the years why such an all-encompassing sonic experience has been denied us. Apparently our patience is about to be rewarded.

If and when the history of 4-channel sound is ever written in the future, several individuals and firms will be mentioned as having been responsible for this new interest in 4-channel sound.

There will be those, too, who will skeptically maintain that this new approach to home music listening is nothing more than a sales gimmick thought up by greedy manufacturers intent upon selling "another pair of everything."

These skeptics simply haven't heard total surround stereo. To hear it is to realize what has already become a cliche in this brand-new technique: "the difference between. 4-channel and conventional stereo sound is perhaps greater than between 2-channel stereo as we know it and monophonic reproduction."

Vanguard Recording Company and Acoustic Research, Inc., must be credited with stimulating the initial new interest in this field.

In cooperation with FM radio stations WGBH and WCRB in the Boston area, these two firms have been sponsoring a series of live symphonic concerts utilizing the regular subscription series of the famed Boston Symphony Orchestra.

Figure 1 illustrates the layout of the four loudspeakers and the two FM stereo receivers required in a home listening situation. Two things are apparent when you examine this figure.

A great deal of equipment is needed and the distribution of 4-channel information is very odd.

When we first saw this diagram we questioned the wisdom of putting the front-left and rear-left on one FM station while the other station carried front-right and rear-right information.

What sort of a lopsided program would the listener equipped with only one stereo receiver hear ?

Recently we had an opportunity to discuss this problem with Mr. Richard Kaye, one of the directors of participating station WCRB. Once he explained the microphone placement used in the concert hall and diagramed in Fig. 2, we realized the nature of the problem.

Had WCRB elected to broadcast front-left and front-right and relegated the rear-left and rear-right to cooperating station WGBH, can you imagine the phone calls that WGBH would have received from its irate listeners?

The microphone placement shown in Fig. 2 was an attempt to offer all things to all listeners. While the left two microphones were designated as left-front and left-rear, the left-rear microphone was, in fact, considerably further to the left than the left-front and only four or five feet behind it.

The same arrangement applied to the two right microphones. In this way, it was hoped that a listener equipped with a single stereo receiver would still experience a fair amount of separation, while the hearty souls able to set up dual stereophonic systems would experience some of the ambient qualities of the symphony hall - the avowed purpose of the 4-channel experiment in this instance.

Listeners have been most enthusiastic, but we wonder if this enthusiasm is prompted by the novelty of the 4-channel listening experience rather than by its state of perfection.

Beginning October 26, 1969, New York City audiophiles were able to duplicate the experience of the Boston listeners.

Harry Maynard, host of the popular "Men of Hi-Fi" program broadcast weekly over WNYC, has crusaded for 4-channel stereo. With the assistance of members of the New York Audio Society who helped to publicize the broadcast and the cooperation of radio stations WNYC-FM and WKCR, (WNYC-FM is the municipally run broadcasting facility and WKCR is operated by Columbia University), 4-channel stereo broadcasting is a regular event in the New York City area. Unlike the Boston experiment, however, the channel arrangement is as shown in Fig. 3.

Admittedly, WKCR must be making a supreme sacrifice in agreeing to
carry just the rear-right and rear-left channels. As of this writing we don't know what the reaction will be from listeners attempting to tune in to WKCR on Sunday night at 10 p.m. utilizing either a single monophonic FM receiver or even a conventional 2-channel stereophonic receiver.

Those of us involved in the New York experiment felt, however, that this microphone arrangement will provide greater impact for 4-channel listeners than would be possible with the Boston arrangement.

It is apparent, I think, that both arrangements have serious limitations. We are reminded of similar compromises that took place in the mid-1950s when early attempts at stereophonic broadcasting were confined to AM/FM combinations.

True, the problems inherent in those early experiments were even greater, since the quality of the AM channel was so inferior with respect to noise and frequency response.

Although the current experiments at least involve all-FM transmission, there do exist somewhat more subtle problems, such as: phase relationships between the cooperating stations, distances from each transmitter to a given receiver, compounded multipath effects, etc.

As was true in the 1950s, a better way will have to be found. William S. Halstead, a noted pioneer in the field of multiplex FM (and one of the many system proponents for stereo FM in the late 1950s), and myself, have proposed at least one solution to the problem.

Before describing our proposal, I would like to make it clear that this is by no means the only method possible. When 2-channel stereo FM was being considered by the FCC, some 17 systems were proposed before the presently adopted system was approved.

• Anmerkung : Es gab demnach also 17 verschiedene Entwicklungen, Stereo Rundfunk zu senden.

We have no doubt that others will come forward now as well. In any event, the system we are proposing does work, permits a single FM station to broadcast four distinct channels of information simultaneously and (subject to certain qualifications which will be discussed in a moment) is compatible with the requirements of effective 4-channel musical reproduction as we presently understand them.

Figure 4 shows presently approved spectrum distribution of a single FM channel engaged in stereo and SCA (background music, etc.) transmission.
.

• Anmerkung : Die US-FM-Stereo Variante ist anders als bei uns in Europa. Dort wird über einen eingebetteten völlig separaten Kanal (SCA) eine ununterbrochen laufende (kostenpflichtige) Mono-Hintergrundmusik für Kaufhäuser und Gaststätten mit übertragen.

.
Main-channel (das Mono-Summensignal) material occupies the range from 50 to 15,000 Hz.

The stereo pilot subcarrier can be seen at 19,000 Hz, modulating the main carrier approximately 10 per cent of the total.

Stereophonic (L-R) information is contained in the range from 23,000 to 53,000 Hz. Finally, the SCA subchannel is located at a nominal frequency of 67,000 Hz and since it is an FM subcarrier, is seen to occupy the total range from 59 kHz to 75 kHz.

The presence of the private-subscriber SCA subchannel necessitates a reduction in deviation of the main and stereo subchannels to a maximum of 80%. Thus, total deviation consists of 80% main and stereo subchannel, 10% pilot carrier and 10% SCA.
.