SPECIAL 20TH ANNIVERSARY SECTION--THE FUTURE OF AUDIO TECHNOLOGY
by ROY ALLISON
ALMOST exactly coincidental with the first issue of STEREO REVIEW (then Hi-Fi & Music Review) I committed to print an assessment of the high-fidelity industry's growth up to that time and ventured a few predictions of what was to come. It was an appropriate time for such an appraisal, because technological developments were then in the process of making profound changes in hi-fi systems.
The first of these was the introduction of transistors in place of tubes for electronic amplification. Even though the solid-state devices of twenty years ago were unreliable and incapable of survival in high temperatures, it was clear that they would become an important factor in preamplifiers and tuners-and eventually, perhaps, in power amplifiers! I took a seat far out on a limb and suggested then that we might soon have amplifiers as powerful as 200 watts. Of course that kind of power is now taken for granted in receivers; power amplifiers are pushing the 1,000-watt mark. At this point we may well pause and ask how much longer the horsepower race can go on. It seems to me doubtful that we will ever be able to use much more than 500 watts per channel at home. Eardrums should not be asked to tolerate more even if loudspeakers can now be made to do so.
That is not to say there is no room for further progress. Semiconductor technology has brought us high-fidelity electronics products whose compactness, convenience, and performance-to-cost ratios simply could not have been achieved with vacuum-tube circuits. In creased use of IC, LSI (large-scale integrated circuits), and digital techniques can bring us further vast improvement. Those who urge a return to tubes are asking us to follow them down a blind alley; the future is not there.
THE second of those fundamentally important events two decades ago was the introduction of stereo on disc records, which required two loudspeaker systems rather than one. And the third was in loudspeaker-system design. Up to then there had been a few very large, very expensive speaker systems avail able which offered reasonably good sound, but the performance of systems small enough to fit in most living rooms and inexpensive enough for most people to afford was abominable by today's standards. Those run-of-the mill "systems" were not systems at all; they were general-purpose drivers in general-purpose boxes.
THE FUTURE OF AUDIO TECHNOLOGY
Edgar Villchur's acoustic-suspension system brought about a neat-revolutionary change. By designing the woofer and its enclosure e.s a unit system, he was able to obtain deep, flat, low-
distortion bass frog: a system of reasonable size and coe'.. When the first is sue of this magazine appeared, the acoustic-suspension system was rapidly gaining popular approval. Soon other manufacturers began making similar systems, and with the establishment of stereo success was guaranteed.
ONE important impetus in the continuing improvement of loudspeakers at very low frequencies is the increased understanding of mechano-acoustical principles among designers as a result of recent theoretical work done in Australia by Neville Thiele and Richard Small. They laid the foundation for de sign by synthesis: that is, they reduced the relationship between enclosure size and type, low-frequency response shape, efficiency, and woofer parameters to a set of relatively simple formulas. The low-frequency design process need no longer be empirical; it can be a matter of straightforward applied mathematics. This has led to the so called "computer-designed" system.
Computers do not "design" loudspeaker systems, of course. They merely do the calculations that would otherwise have to be done manually. And this new design technique does not extend the range of woofer performance beyond what was always possible. It does, however, make it easier for a designer to achieve best results in each case, as well as more likely that he will do so.
It would be foolish to say that any further refinement in basic loudspeaker performance must be incremental.
However, I believe that the really important new work will be the result of ex tending the "system" concept further to include the listening room itself. Already there is movement in that direction. The major effects that reflections from near by room surfaces have on loudspeaker-
system performance below 500 Hz, for example, have recently been defined and quantified, and they can now be reliably taken into account in a loud speaker system's design. In a real sense this is combining the speakers and the room so that they can be considered as one transducer system.
A step toward neutralizing the listening room's own acoustic properties has been taken with multiple-channel systems beyond stereo-first with four-channel systems and now more successfully with time-delay ambiance-synthesis systems. Undoubtedly this kind of thing will be developed far beyond its present level in years to come. Significant improvement has al ready been reported when time-delay systems are extended from the normal two rear-channel speakers to four or more, each with differing ambiance in formation. More sophisticated systems will be devised with which the listener can program any acoustical environment he desires.
---Roy Allison went from a career in audio and electronics journalism to a series of major positions with Acoustic Research in 1959. He now heads his own company, Allison Acoustics, an organization prominent in loudspeaker research and design.
It is fortunate that there is this steadily increasing recognition of the crucial role of the listening room, the last link in the sound reproduction chain. A better understanding of how it can be incorporated into the system design as a whole will surely produce enormous benefits in the future. The day is coming when we will be able, finally, to produce a consistent illusion of really "being there."
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EDGAR VILLCHUR
"Quadraphonic systems appear for now to have enjoyed a solid market failure, but they represent the direction in which high-fidelity design needs to go for non-electronic music."
Edgar Villchur, founder and prime mover of
Acoustic Research, developed the acoustic-suspension speaker system, the
dome tweeter, and the now-classic AR turntable. He presently heads the nonprofit
Foundation for Hearing Aid Research.
IN considerably more than twenty years' involvement with audio, I have always felt that a sound-reproducing system ought to re-create, as accurately as possible, the original musical sound as it is shaped by the acoustics of the concert hall or studio. But I realize that this goal is not suitable for all music. For example, standards of tonal accuracy do not help much in evaluating high-fidelity equipment when electronic music is being played, because we don't know what original sound the reproduction is, supposed to be faithful to. The original is an electrical wave form produced by a vibration pickup or by an oscillator, and it doesn't become sound until it is fed to a loudspeaker.
Under these circumstances the evaluation of sound equipment involves judgments that have more to do with musical taste than with musical accuracy.
However, for "old-fashioned" musical instruments-the kind that can be played without being plugged in accuracy is a reasonable goal. The traditional task of a reproducing-equipment designer is to eliminate or at least to minimize any coloration imposed by the equipment. The overall record/ reproduce system should also be de signed to reduce coloration imposed by the listening room. It is the listening room and not the loudspeaker that is the last stage of a reproducing system, and a typical living room has poor musical acoustics for even a small instrumental group. The listener must be freed, at least partly, from the acoustical environment of his room and given a sense of concert-hall or studio acoustics. Wide-dispersion speakers, careful speaker placement, and speaker de sign that takes room acoustics into ac count have all helped, but the major factor that has contributed to conveying a sense of the original environment of the recording was the introduction of stereophonic reproduction.
Now we have gone a step further in the business of simulating concert-hall ambiance in the living room with quadraphonics and the rear-delay systems.
Quadraphonic systems appear for now to have enjoyed a solid market failure, but they represent the direction in which I think high-fidelity design needs to go for non-electronic music. As for the failure, it may have been deserved. With one or two exceptions, the quadraphonic systems I have heard sounded like four mono systems going at the same time, creating an expanded version of ping-pong stereo. Sound reflections in a good concert hall or studio never give the impression that the reflecting surfaces are separate sources of sound.
One is conscious of the reflected sound only in the acoustical ambiance that colors the music. In Contrast, these quadraphonic-system configurations and/or recordings give an independent existence to the sound from the rear loudspeakers, perhaps to assure the listener that he is getting his money's worth. If a rear-speaker system is to be successful it must convey a sense of the acoustical environment of a concert hall or studio without making the listener aware of any separate sound from the rear. Otherwise it is only a gimmick.
MORE than a decade ago I made a re cording of the Fine Arts Quartet for the purpose of staging "live-vs.-recorded" demonstrations. The recording had to have as little reverberation as possible in order to avoid double reverberation during playback-that is, reverberation from both the recording environment and the playback environment. The mu sic was therefore recorded in an open, outdoor location. In a concert hall the sound of the recording reflected the beauty of the quartet's tone color, but in my living room the same tape had a hard, over-bright quality. A live string quartet doesn't sound good in my room either, and neither the tape nor the playback system introduced a substitute acoustical environment. A recording must transport the listener to a con cert hall, not crowd the musicians into his living room.
Earphones eliminate room acoustics, and they can be used to help solve the problem of a musically unsuitable listening environment. But they are not acceptable for all occasions or to all persons. One of the problems in sound reproduction that has not yet been fully solved is how to bring concert-hall ambiance to living-room listening. But we are still trying, and maybe we are coming closer.
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DANIEL VON RECKLINGHAUSEN
EVER since the invention of the phonograph one hundred years ago, public demonstrations of audio reproducing equipment have been made claiming-and often convincing listeners--that the reproduction matched the original "live" sound. However, al though each new demonstration showed improvement, the truth is that in spite of all efforts, music reproduction in the home is not perfect. The concert hall or the stage has not yet been brought into the home in a form indistinguishable from the original sound. This lack of perfection gives all of us involved in audio opportunities to improve. A few examples may show possible future trends in combating the problems that still stand in the way of perfection.
THE reproduction of sound in dwelling-size rooms suffers from several ailments, such as resonances that fall well within the audible range and noise problems for listeners and for their neighbors. A likely solution may be a wearable device, similar to head phones, containing sound-reproducing diaphragms plus a microphone near each ear to eliminate most of the external noise by means of acoustical-cancellation techniques. This would pro vide more wearing comfort than the tightly sealed, heavy, and restricting acoustically isolating headphones available today. Such a device should also be capable of reproduction of high sound-pressure levels yet contain safety circuits to prevent hearing damage.
The principal advantage of a multi-loudspeaker sound system is the possibility of the creation of sound images in various locations in the room. Unfortunately, the supposedly fixed imaginary sound sources move as the listener moves. As many acousticians know, spectacular sound reproduction at the listener's ears can be achieved using a high-quality headphone to play recordings made with two microphones placed in an artificial head. Yet even this technique leaves something to be desired. As long as the listener is immobile, the acoustic images are in their proper position, but as soon as he moves his head the images move (un naturally) with it. This problem could be avoided if the listener's head movements caused the artificial recording head to move as well. A fertile imagination might then conjure up the vision of a concert hall full of artificial heads, each moving under control of its connected listener.
The number of transmission channels required and the resulting costs would be staggering, and the technique would still be applicable only to a live performance. But perhaps one solution might be the radiation of three or four audio signals (from live performances or recordings) using multiple modulated-light sources distributed throughout the room. Partially shielded photo sensors attached to the listener's headphones would pick up and decode the multiple light sources with correct directionality maintained.
This would make it possible for several listeners each to achieve a different program "mix." Within the next decades, digital audio equipment will be used, in the home for high-quality sound reproduction and processing. Such equipment will be vastly more complex in circuitry than the equipment we now use. The growth of this field of entertainment electronics will depend strongly on the cooperation between equipment producers and pro gram producers. Meanwhile, records and tapes will continue as program sources because of their relative simplicity, and AM (expanded to stereo) and FM (possibly in three- or four-channel form) radio should also persist.
DIGITAL recording and transmission of audio signals will require agreement on a digital code. The code will involve as signing a group of digital "bits" to a particular level of voltage, with each instantaneous variation requiring a different code "word." (If agreement is not reached, a situation similar to the stale mate in video recording could happen, where various methods of video disc re cording coexist but lack interchange ability.) The digital-bit stream representing the audio signal will be controlled by a computer, the heart of the audio system. Control of volume will be the multiplication of each digital code word by a constant factor, while mixing will be digital addition and subtraction.
Needless to say, the controls of such audio equipment will look more like a calculator or typewriter keyboard than the profusion of knobs and switches we know now.
In the next few decades more signals will be broadcast and the broadcast spectrum will be more and more crowded, placing more demands on receiver and tuner performance. Perhaps a new class of tuners will emerge: "adaptive" tuners that adjust their selectivities and noise-reducing circuits in response to the actual signals encountered. Such devices may also reduce distortion caused by multipath reception of a signal by generating multiple delayed signals which can then be subtracted from the total signal to cancel the multipath electrically. Such a tuner will require multiple analog or digital delay lines to create these delays.
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--- "Digital recording and transmission of audio signals will require agreement on a digital code. . . . If agreement is not reached, a situation similar to the stalemate in video recording could happen." ---
Daniel von Recklinghausen joined H.H.
Scott, Inc. in 1951 and guided that company's high-fidelity research and
development efforts during its most eminent years. He is now vice president
for research and development at KLH.
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With luck, the digital audio equipment of the future will not only be better, but also less costly. The rapid drop in calculator prices over the last decade gives us hope for that. Possibly all audio systems and techniques will reach a plateau of excellence in the next few decades, removing the pressures of innovation from designers and affording them more time to correct the deficiencies of the "perfect" equipment they have devised.
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ETSURO NAKAMICHI
"The coming generation of audio products will bring astounding new levels of technological achievement, but they will also demand more than ever before of the audio consumer."
Etsuro Nakamichi manufactured high-quality cassette
decks for a large number of well-known hi-fi companies until, in 1972, he
introduced his own Nakamichi Research brand name. His research center in Tokyo
is a showplace for both advanced cassette technology and live music.
SOME exciting and surprising developments lie in store for the near fu ture of the audio industry. There will also, however, be much confusion and disillusionment in the high-fidelity marketplace. These statements may seem contradictory, but they are, I believe, in escapable conclusions. The coming generation of audio products will bring astounding new levels of technological achievement, but they will also demand more than ever before of the audio consumer. It will take a highly knowledge able, acutely perceptive buyer to recognize the difference between true engineering breakthroughs and the machinations of artful marketing experts.
As supply begins to outstrip demand, competition (especially among the Japanese manufacturers) will become increasingly fierce, and the consumer will be faced with the task of selecting his equipment amid a multitude of seemingly fantastic technical specifications and performance claims.
What are some of the technical innovations one can expect to see in consumer audio products within the next few years?
GREAT equipment design during the past few years, and I predict further significant improvements in this area. The wide spread use of more sophisticated measuring equipment, such as the narrow-band spectrum analyzer, has predictably raised the general level of audio performance. Distortion and noise are several orders of magnitude lower today than they were just a few years ago. But, more important, new measurement techniques have given UF a better understanding of what makes one component sound better than another. It was gratifying to me, for example, to have the narrow-band spectrum analyzer confirm my long standing conviction that small-signal linearity has a tremendous effect on perceived sound quality. Before this remarkable test instrument came into existence, low-level signals defied measurement because they were invariably buried in noise. Further experimental and theoretical work being done on equipment design today will undoubtedly come into bloom as the products of tomorrow. Components of the not-too-distant future will not only measure better but sound, significantly better as well.
The field of magnetic tape recording will most probably be an arena for exciting improvements and innovations. Microprocessors have already begun appearing on a number of tape-recording products; microprocessor-controlled systems will undoubtedly become standard features shortly.
There is much speculation about the appearance of tape decks utilizing digital recording processes, such as the PCM (pulse-code modulation) system.
My honest belief is that digital recording still has a very long way to go before it appears on the market. True, a number of notable Japanese firms have exhibited various PCM recorder prototypes at recent shows, but all such prototypes were, without exception, produced at extremely high cost. PCM and other digital signal-processing techniques, furthermore, are still suffering from a number of technical deficiencies despite impressive claims for dynamic range, frequency-response linearity, and distortion. Although exact causes are yet to be determined, it would seem that digital recording systems are experiencing difficulty in gaining the endorsement of critical listeners. Just as the earliest sol id-state components were criticized for what was later termed "transistor sound" there is already talk in audio of "digital sound" as the major shortcoming of systems such as PCM. Considering the very high cost of present digital recording systems, and the fact that even in this day and age a small minority of audiophiles still believes vacuum tubes "sound better," I think it would be misleading to suggest that a sonically satisfactory and reason ably priced digital tape recorder is just around the corner.
As a manufacturer who has built his, reputation on cassette-deck technology, I feel that the most exciting and immediate innovations in magnetic tape recording lie in the areas of new tape formulations, improved magnetic heads, and more effective noise-reduction systems. New tape formulations and magnetic heads, both of which take advantage of radically new metal alloys and manufacturing techniques, already exist at an experimental level and provide a dynamic range far in excess of what can be attained with' today's top-of-the-line products. I believe that within the next few years these advances will be introduced on cassette decks primarily aimed at the professional and semi-pro market. With the aid of new noise-reduction systems, these cassette decks will attain dynamic-range figures unattainable with even the best of today's open-reel recorders.
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HENRY KLOSS
I BELIEVE chances are good that the I more important developments in audio's future will come from television. After all, every home has one or more TV sets, and the TV industry has ample financial resources for vast new development projects.
Specifically, what could happen is the coming into our homes of a multiplicity of wide-band information channels--channels capable of carrying a video signal. It's only logical to assume that some of those channels will be used for audio, whether they're beamed down, multipath-free, to a little dish antenna on your roof from a satellite, or whether you recover them from a special disc recording. That could change the picture for the "front end" (the signal-recovering components) of audio systems in twenty years. Audio signals may well come from the "TV set" and other devices designed to handle video signals. And that means that audiophiles (and magazines like this one) will have a lot less to worry about: if the set is designed to broadcast, receive, store, and recover video, that will end any further discussion of such problems as audio bandwidth and signal-to-noise ratio in this part of the system.
ONCE the audio signal is recovered, it will more than likely be fed to reproducing equipment that doesn't differ all that much from what we have today. Nearly twenty years ago, when you went into a hi-fi shop for a stereo system, chances are you came out with something like a Scott 299 amplifier, a pair of KLH 6's or AR-2's, and maybe a Garrard changer or a Rek-O-Kut turntable. Today, for the same few hundreds of dollars (and without even taking inflation into ac count), you walk out with something with a wider frequency range, lower distortion, no rumble, greater reliability, and so on. That's just remarkable, but the configuration of today's system re mains pretty much the same. And the improvements have as much to do with economics and competition as they do with new technology. But how many zeros do you need after the decimal point in a distortion specification? Perhaps a hundred-watt-per-channel amplifier can be made to fit into the palm of your hand, but whatever for? You've still got to put the knobs somewhere, and even now our fingers can barely find their way around the buttons on those little calculators.
There's also the whole area of signal processing, a topic that particularly fascinates me. But there's one question that has yet to be answered about such devices: how hard will people be willing to work at getting a desired effect or sound quality? Today, for example, there are a number of equalizers that can be really effective, but I suspect that the reason they're being sold is mostly that they are there to be bought.
AND finally there's the whole matter of synthesizing in the living room the acoustics of a much larger space-an idea that has occupied a small corner of my mind for the last twenty years. The bits and pieces are now out there finally-that will enable us to put some thing together that's really convincing.
But while we don't need as many speakers around the room as there are reflecting surfaces in the concert hall, I can see no way of getting around the need for significantly more speakers than the one additional pair now being used for quadraphonic sound. Will a significant number of people be willing to work hard enough to get things sounding right to warrant somebody's developing such a product? I certainly don't know the answer to that one. But perhaps there will continue to be for the next twenty years-as there have been for the past twenty those in the audio industry willing to take the trouble to find one.
"Perhaps a hundred-watt-per-channel amplifier can be made to fit into the palm of your hand, but whatever for? You've still got to put the knobs somewhere."
Henry
Kloss, founder of Advent Corporation, has been prominent in the histories
of both Acoustic Research and KLH, of which he is the "K." Mr. Kloss,
who developed the Advent Videobeam," is now independently engaged in further
projection-television research.
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PETER GOLDMARK
"One fact that has to be faced is that there may be a saturation point for passive entertainment; if there is, we're not very far from it."
Dr.
Peter Goldmark, best known to the audio world as the developer of the LP
record, actually spent most of his illustrious career in the area of video
and television. Until his recent death he directed Goldmark Communications
in the manufacture of video program materials for commercial users.
WE tend to look upon the potential popularity of home video recordings as a great unknown. It's like a multi-dimensional puzzle, and you have to consider a number of segments or pieces. One of these has to do with pure enjoyment content vs. money spent. How much of his dollar will the consumer allot to a recording (video) he knows he will view perhaps only once or twice, as opposed to a recording (music) that he knows from experience will give satisfaction for many replays? Another factor is competition. More and more movies are being shown on the air by the national networks, and one of the reasons is that they are being used to counteract the increase in popularity of pay TV over cable. I suspect that the national broadcaster, with his enormous market, has not yet really begun to flex his muscles. When he does, it's possible that the owner of a home video player, after an initial period of infatuation with the novelty of it all, will decide that he's investing his entertainment dollar in the wrong place and return to broadcast TV. Of course, we cannot yet take into account the effect of commercials and the editing that so many broadcast movies are subjected to.
This is another unknown.
One fact that has to be faced is that there may be a saturation point for passive entertainment; if there is, we're not very far from it. There is simply so much to see and so little time to see it. Furthermore, we cannot automatically expect the consumer to make a practice of taping material off the air for later viewing. For some reason, taping off the air is not the great indoor sport in the U.S. that it is in Europe. Also, who is to say that the "later viewing" will ever take place? By that time there will be new material competing for the con sumer's time.
OF course, there is the hope that the home video medium will be able to compete by offering hitherto unavailable program material: informational or educational programs, for example, things that will help a viewer improve himself in his job or in a sport, assist in hobbies or other self-improvement. The programs of this type now offered by the national broadcasters are few, and the viewer has no control over them.
Spectator sports is another area that al ready shows promise. One can imagine, for example, a videotape album containing all the winning performances from a season's Olympic Games.
One program possibility often suggested-and one about which I am frankly a little dubious-is the rock spectacle or live popular-music concert.
My own children have, attended events such as this, but it seems to me that what they seek is the excitement of an experience shared with thousands of people simultaneously, plus the opportunity to share the live presence of their music heroes. Whether a home medium can succeed in supplying anything like that ambiance is questionable. It may well turn out that the audio part of the program will prove much more important in such a production, leaving the video portion with a very subsidiary role.
(Note that although there are some rock programs on TV, they are mixed with a great deal of variety material. You never see just what you'd experience in Madison Square Garden during a rock concert.)
IN any case, there are going to be quite a few TV sets with videotape recorder-players coming on the market this sea son. This will be a sort of test, because it may show what the consumer appetite is out there-where it is, and how big it is. It may also show how much money people are willing to invest in home video. I admit that the tape player and the video program on the tape will amount to a fairly expensive package, but it shouldn't be overwhelming. In general, something like a two-to-one ratio of costs-video materials vs. present home-entertainment media-can be expected. If the attractions of the medium's content can successfully off set its cost, video may yet find a home with the consumer.
I do not yet, by the way, see any signs that my own children are making a special adaptation to video technology. They all like to listen to music, but otherwise they identify communications like everybody else-with entertainment or filling some informational need.
We do not have a video machine of any kind at home, and there seems to be no demand for it in the family as yet. What do we turn to for entertainment? Well we have an enormous collection of disc recordings ...
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Also see: I Remember Mono--An Audiobiography
Source: Stereo Review (USA magazine)