PAPER CHASE
As most readers of Audio know, the Audio Engineering Society holds two conventions each year, one in this country and one in Europe. Several special regional conferences are also convened on specific subjects of interest to audio engineers. While the main conventions feature exhibits of glittering new audio equipment, mostly professional, the serious business of AES conventions is the presentation of papers that cover virtually every aspect of audio science and technology. Naturally, these papers reflect the trends and developments in current audio interests. Of course, in recent years digital audio has been predominant and will likely remain so for the foreseeable future.
Every aspect of digital audio is being assiduously researched in laboratories throughout the world.
The success of an AES convention is judged not only on high attendance and the number of product exhibitors, but also on the number and, most especially, the quality of the papers presented. Over the past few years, the papers have been remarkably consistent in their high quality. By and large, these papers are written by some of the most brilliant scientists and engineers in audio. As you might expect, many of these papers cover some of the most arcane and complex areas of audio, and are quite beyond the ken of most audiophiles. Yet at nearly all AES conventions, a number of papers are presented which have relevance to the well-rounded audiophile. They often provide deeper insight into a subject than does the literature generally available to him.
At the recent 87th Convention of the AES in New York City, I spotted several papers which should be fascinating reading for the audiophile with an inquiring mind. Preprint No. 2850 (D-2) is "The Influence of Room Acoustics on Reproduced Sound, Part I: Selection and Training of Subjects for Listening Tests." This covers some of the research activities of the Archimedes Project, a joint effort of the Technical University of Denmark, Bang & Olufsen, and KEF. There is fascinating information here on the selection of subjects, who must meet certain criteria of value in conducting repeatable, statistically significant listening tests on loudspeakers. Understandably, the Technical University's Acoustics Laboratory wants people with normal hearing to participate in these tests-but what is "normal hearing"? As this paper so succinctly puts it, "An otologically normal person is a person in a normal state of health who at the time of testing is free of excess wax in the ear canals, is without known ear pathology, and has no history of undue exposure to noise." (Obviously, this precludes boilermakers and devotees of rock concerts!) Potential panelists are asked many pertinent questions with respect to their audio equipment (if any), listening frequency and duration, music preference, frequency of attendance at live concerts, etc.
Preprint No. 2825 (D-8), "Sound Quality Assessment: Concepts and Criteria," is by Tomasz Letowski of Penn State University. The author states, "Although the concept of sound quality is widely used, the term itself is not clear and does not have a precise meaning. Such a situation causes various conceptual and practical problems. In addition, despite a large number of terms describing sound character, these terms do not form a system of well-defined and clearly linked perceptual parameters. Such a system and several related definitions are discussed here." Needless to say, this particular paper is required reading for those reviewers given to florid and fanciful terminology when describing sound quality! Preprint No. 2874 (W3/5-E), "In-the Ear Recording and Pinna Acoustic Response Playback," by my pioneering friends Don and Carolyn Davis of Synergetic Audio Concepts, discusses an exciting concept in the ongoing quest for a closer approach to reality in recorded music. In the ITE/PAR system, the ears of a live person, rather than a dummy head, are used as a "human microphone." This is accomplished via special clinical microphones whose soft silicone probes allow recording in the pressure zone of the eardrum. The signals from these low-noise, wide-frequency-range, wide-dynamic-range microphones are stored on a DAT recorder. Playback is via the PAR geometry, which uses synchronized loudspeakers in front of, and to each side of, the listener's ears. No pun intended, but this is heady stuff, with interesting implications for the future.
It is obvious that more and more people are setting up home theaters for the reproduction of Dolby Surround films via videocassettes and laser videodiscs. Stereo surround broadcasts on TV are also becoming fairly common. Preprint No. 2855 (G-6), "Stereo-surround-A Compatible Multichannel Encoding/Decoding Process for Audio and Audio/Video Applications," affords a good overview of surround sound technology and a look at special applications developed by engineers at Shure. You'll note in the title that "audio" is treated separately from "audio/video." This is because the stereo surround processing detailed in this paper can be straightforwardly applied to music recording, without any video involvement. I can tell you that a fairly prominent small record company is seriously investigating the use of this process in specialized CD recordings.
Finally, one of the most important papers given at the 87th Convention is Preprint No. 2872 (W2-A), "Fiber Optics: The New Medium for Audio," by Ronald Ajemian and Albert B. Grundy.
This was actually a workshop and tutorial on fiber optics, featuring really fascinating demonstrations. I can assure you that fiber optics is currently very important in audio and will absolutely be a major factor in digital audio and video in the not-too-distant future. Even if the previous preprints do not interest you, I urge you to acquire this one.
Yes, it is that important, and reading it will provide a basic understanding of this seminal development, which is having a profound effect on audio/video technology. The paper outlines the historical background of light transmission, which, surprisingly, goes all the way back to 1870! Parts of the preface to this paper are worth quoting: A Nobel Prize was awarded to Arthur Schawlow and Charles H. Townes for developing the laser, which was first successfully operated by Theodor H. Maiman in 1960. Then the manufacturing process of lasers from semiconductor material was realized in 1962. At the same time, semiconductor photodiodes were developed for receiver elements.
Now the only thing left was to find a suitable transmission medium.
It finally happened in England in 1966, when Charles H. Kao and George A. Hockham of Standard Telecommunication Labs published a paper proposing that optical fibers could be used as a transmission medium if their losses could be reduced to 20 dB/km. They knew that high losses of over 1,000 dB/ km were the result of impurities in the glass, not of the glass itself. By reducing these impurities, a low-loss fiber may be produced for telecommunications.
Finally, in 1970, Robert Maurer and associates at Corning Glass Works developed the first fiber with losses way under 20 dB/km. And by 1972, lab samples were revealed as low as 4 dB/km Since then, Corning Glass Works, Bel Telephone Labs, and also Nippon Sheet Glass Company of Japan have developed glass fibers with losses at about 0.2 dB/km. There is also research being done with plastic materials as well as glass.
As you know, thousands of miles of fiber-optic cables are now in place in the telephone companies' networks. In Cerritos, Cal., a suburb of Los Angeles, some 600 new houses are having fiber-optic links to the telephone companies' fiber-optic networks installed.
At present, such links cost about $3,000, but as with most innovations, widespread use will eventually make them more affordable.
It is important to recognize that in the next few years, digital technology will play a major role in the daily lives of the American consumer. Home entertainment (both audio and video), information systems, interactive banking and shopping, and a host of other services will be available in digital format-all through the miracle of fiber optics. A computer terminal in the home will control this multitude of services. Envision, if you will, a centralized CD and videodisc library of virtually every recording in existence. (The library would be equipped with the very best playback systems.) In practical use, a person could simply punch a code into his home computer to choose whatever music or video he wanted. The music would then be played through his audio system, interlinked via fiber optics, and he would look at the video on his digital high-definition TV. If all this sounds like some science fiction vision of the future, it most assuredly is not. At the upcoming Summer Consumer Electronics Show, it is quite likely that one company, and perhaps several, will introduce fiber-optic systems to interlink audio components such as amps and preamps. These components will, of course, have their own A/D and D/A converters. Initial cost for such systems could be around $1,800 to $2,000-not out of line with some of the very expensive, exotic audiophile cable now on the market. The advent of fiber-optic interconnects should finally put an end to the often fanciful performance claims made for audiophile cables.
The preprints I have discussed are available from the Audio Engineering Society, 60 East 42nd St., New York, N.Y. 10165. Each preprint costs $5 for nonmembers, $4 for members.
(adapted from Audio magazine, Mar. 1990; Bert Whyte)
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