SIGNALS & NOISE (Letters to Editor) Jan. 1985

Credit Account

Dear Editor:

I have yet to hear the CD of The Rolling Stones' Tattoo You, but judging from the analog disc I'm sure it would generate all the aural excitement praised by Paulette Weiss in her review in the November Audio. But please, credit where credit is due! Nearly all the sonic effects she praised were the work of mixing wizard Bob Clearmountain, a Wunderkind who does similar work for Bruce Springsteen, Huey Lewis and The News, and Hall & Oates, among others. Bob is a modest guy who accepts his name in small print, but sometimes small-print names step out in front of the big-name stars. Apparently this CD is a case in point.

-Sam Borgerson; Studer Revox America; Nashville, Tenn.

Suffering Comparisons

Dear Editor:

Audio does some of the best equipment tests I have seen. The record reviews are excellent too, and at least you do more CD tests than most of your competitors.

Your tests of CD players and related gear have had one glaring problem, however. You have yet to do a really comprehensive A/B listening test between competing units. For example, in the September issue, Leonard Feldman claimed the Revox player sounded better than other CD units he had tested. However, he made no direct NB comparison between it and any other, more conventional unit, because he had none available! What does he listen to between tests? Let him compare the Revox, or any other units under test, with that item. Just compare something with something, instead of making vague generalities about how it seemed to sound better than he remembered other units sounding. What kind of science is that? This kind of rigor is necessary in light of growing claims regarding phase distortion.

Does increasing the sampling rate really make a difference? A simple listening comparison between old-style and new-style units, while not giving definitive results (because of limitations in the whole reproduction chain), would give your readers more to go on than simple, vague observations.

Similarly, in your July issue, you printed an article on the Dennesen phase-correction device, written by someone with a vested interest in the unit. Obviously, he thinks it works.

When Richard Heyser had a chance to really test the unit (by really listening to it), we get a set of vague measurements and the comment that he "cannot positively say how effective it is." Why didn't he listen to it in operation? How hard would that be to do? A manufacturer friend of mine tried one out at a hi-fi show, in order to see if it would correct problems with a Sony CDP-101 (this was early in CD history, and the main problem was poor recordings). No one, not even the Dennesen engineer who was there, could hear any difference! Also, some friends of mine hooked up the Revox, a Technics SL-P10, and a Marantz CD-73 and did an A/B/C comparison, using Crown amps and Ohm Walsh 4 speakers. No one could hear any difference, once the outputs were equalized. All players were in sync, and the program was three identical CDs. If rank amateurs can do this kind of test, why can't you guys?

-Howard Ferstler; Tallahassee, Fla.

Pro Analog

Dear Editor:

I wish to comment on Ken Pohlmann's article, "A Binary Beginning," in the April issue. I, too, am an engineer, with much experience in both analog instrumentation and high-speed data acquisition systems, and I found the article very misleading and technically incomplete. First, he would have done well to give a fair and total comparison between analog and digital signal processing capabilities and limitations, instead of just saying "analog is a mistake." The interface of the stylus and conventional disc is the limiting factor. The electronics of a well designed analog block will usually be more accurate, have better resolution, and be less costly than the equivalent digital block. Also, analog techniques have much higher bandwidths.

Digital processing, specifically digital replication of random analog events, such as music, has its share of limitations. As some manufacturers are discovering, the Nyquist sampling theory isn't sufficient for upper audio frequencies, and present 40+ kHz sampling rates are too low. Higher sampling rates may also reduce the complexity of the error correction and other "housekeeping" circuitry. But cost/performance is still a problem--high-speed D/A and A/D converters are expensive. Some interpolation will still be required, however, because, at best, with today's technology, digital sampling techniques give an approximation. Most of the events to be measured or evaluated in the real world are analog in nature, and digital technology serves nicely to interface the real world to computers, but to imply that digital itself is a superior method is totally incorrect. It would be nice to see Audio publish some good "nuts and bolts" articles on the subject so that the readers can get something out of it.

Isn't that what Audio is all about?

-Charles Blaisdell; Essex Junction, Vt.

Author's Note:

I agree that my column, "A Binary Beginning," was incomplete; it is indeed difficult to present a "total comparison between analog and digital signal processing capabilities and limitations" in 1,000 words or less. Otherwise, I strongly take issue with your comments. It is my opinion that analog technology has served us well; however, it is no longer adequate for today's standards of audio recording and reproduction. From an engineering standpoint, music is information, and it is clear that digital technology offers superior techniques for data storage and processing, as has been so dramatically demonstrated by the proliferation of digital computers. Contrary to your statements, digital audio technology is more accurate than analog technology; a comparison of the performance measurements we use to evaluate accuracy in audio components will demonstrate this. Furthermore, with circuit integration, the cost of A/D and D/A converters is now diminished within a system context, a digital system can have higher resolution and bandwidth and lower cost, and present standards for sampling rate and quantization are sufficient for the complete enjoyment of high-fidelity audio and rival the best analog has to offer.

My enthusiasm for digital audio stems from the fact that whereas analog technology has reached its full maturity, digital audio has just been born.

It is clear that both in theory and practice, digital audio is already superior to analog, and in the future only our expectations and understanding of technology's potential will be the limiting factors.

-Ken Pohlmann

CD Potential, LP Reality

Dear Editor:

Bert Whyte's "Behind the Scenes" in your August issue highlighted some rather provocative issues regarding the advent of digital disc technology and, in particular, the role of the audio critic. Having been deeply involved in the development of the phonograph medium for the last 48 years, Shure has naturally taken great interest in the progress of the digital disc. I should like to offer a few comments that relate to Bert Whyte's column and how we at Shure view the future in the phono and digital disc business.

In the phonograph medium, there is a long, complicated process that starts with converting sound into electricity during the original recording and eventually proceeds to the conversion of record modulation into electricity during the playback. At the beginning of the process, the recording technique involves both aesthetic and technical activities to create a master tape. After the master tape has been prepared, numerous processes are employed to create a phonograph record. The latter are purely technical processes, many of which have limitations that can affect the final reproduction.

In each part of the process, a great effort has been made to minimize the limitations. For example, in designing phonograph cartridges, our objective has been to make a product that translates the information from the disc into an electrical signal with maximum fidelity. Similar goals have been set in the mastering and record production processes. Even with those objectives in mind and with the enormous amount of effort and accomplishment that has been achieved in reducing distortion and other effects that would change the quality of the sound, there remain certain limitations in the phonograph process.

Since the chain of functions required to create the entire process is a long one, and since each function has some limitation, it is very difficult, if not impossible, for the audio critic to determine which particular function has affected the reproduction of the sound.

The audio critic must essentially evaluate a finished product. I am always impressed when a critic, such as Bert Whyte, can pinpoint a problem to a factor such as microphone placement. I suspect, however, that even a man with Mr. Whyte's experience can only make that judgment in the case of a fairly significant deficiency.

Hundreds of thousands of LP phonograph records have been created, and, as we know, many of these records are superb and of outstanding aesthetic and technical value. Over the years people have learned how to optimize the phonograph medium in spite of its limitations. The master tapes for those records were created with that medium in mind; simply attempting to reproduce them on digital disc will probably not create a product as satisfying as the phonograph records for which they were intended. What is needed now is an entirely new library of recordings that have been recorded specifically for the digital disc. Development of the library is going to take a fair amount of time because recordings for many years will be made during an evolutionary period in which the technology will be changing. What is recorded today may not be optimum five years from now. It is for that reason that I believe the phonograph medium will be here for years to come.

The potential we see for the digital disc would be the elimination of many of the limitations we now have in the phonograph process (although I doubt that we are at that point at this time). Ultimately, we would hope that the electrical signal that comes out of the digital disc player will be so close to that which is on a master tape as to make the difference inaudible. When that occurs, the role of the audio critic will be essentially one of commenting on the aesthetic and technical quality of the recording technique. At that time, I believe the qualifications for an audio critic will be, as implied in your August issue, that of people such as Bert Whyte and Angus McKenzie, who really understand both the aesthetic and technical requirements of making a recording.

How to judge the quality of a recording is, of course, a personal matter for each of us. If we wish to use the advice of an expert, we depend on a reliable critic. While some of the critics of today can provide purely aesthetic commentary, I am certain that the critic for the ever-improving technology of tomorrow will need to have a strong technical orientation as well. In particular, the critic of tomorrow must have knowledge of microphone technology and the acoustics in the recording process.

-James H. Kogen; President Shure Brothers Evanston, Ill.

Quality Control for CDs

Dear Editor:

I have had my Compact Disc player for a little more than eight months and now have over 100 CDs in my collection. I have noticed some very positive and negative trends occurring with CDs. On a positive note, there is a growing selection of discs for me to chose from. I am also pleased with the more affordable prices; today I pay no more than $12.99 for most discs. And of course, the sound on a well-produced disc is terrific.

The problem which now disturbs me is that more and more of these discs are defective. Two out of the last three I bought this past week would mistrack. (One was a Mobile Fidelity CD.) These discs were sealed when purchased, but upon close examination, I noticed small indentations and scratches as well as more than a normal amount of dust. Even after brushing the foreign particles off a disc, it would still mis track in the same place.

My concern is that with this storage medium that can accurately reproduce the original studio tape, the CD will be treated like any other mass-produced vinyl record. I stopped buying records and started buying CDs to eliminate the problems of dust, bad pressings, and mistracking. I returned the defective discs, but if quality control is not kept at a stricter level, I will be forced to stop buying CDs altogether.

-Michael A. Steinberg; Rosell Park, N.J.

(Adapted from Audio magazine, Jan. 1985)

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