PERFECTING SILENCE

Grounding and Shielding Techniques in Instrumentation, Third Edition by Ralph Morrison. Wiley-Interscience, 172 pp., hardback, $29.95.

Noise Reduction Techniques in Electronic Systems, Second Edition by Henry W. Ott. Wiley-Interscience. 426 pp., hardback, $39.95.

For many years, I used an earlier edition of Grounding and Shielding Techniques in Instrumentation to solve problems, and I have advised many students to refer to this book for help when their electronic systems show residual noise, hum, and interference.

Recently, I was most pleased to be introduced to Noise Reduction Techniques in Electronic Systems since few books are available on the important subject of shielding, grounding, and noise and interference reduction.

The problems addressed by these books are rarely discussed in formal classes at universities or technical schools. Reducing residual noise in a system which is supposed to have a very large S/N ratio has often been left to the engineer or technician on the design team who seems to understand this "black art." There is always some noise remaining in any electronic sys tem, and it is too often left for the final tweaking stage of the design. The problems are usually "solved" by moving ground connections internally, changing a connector or a cable, adding a wire or shield, moving a part or subcircuit, or some similarly mysterious and chancy technique.

It should not be necessary to proceed in such haphazard ways. There is, and always has been, a science behind these black arts. I must say that both of the books under review here are very good introductions to the methodology of removing noise and getting the signal from the source to its destination without contamination.

The topic of lowering the residual noise of electronic systems is important in the design of all types of equipment and is of especially great importance to the audio engineer. The ear is very sensitive to residual noise be cause of its great dynamic range, possibly 120 dB or so. This range is almost as great as that of well-designed electronic equipment. The issue of residual noise and interference is more important than ever these days because of the quality of the Compact Disc. Its extended dynamic range, in has made the audio listener ever more sensitive to the quality of the silence between musical passages. This level of silence is attained sonically only by the most careful design of the electronic circuits, their precise mounting and shielding within the chassis or box, the quality of the box design and the connectors, the use of correct wiring techniques, the exact placement of trans formers, and a seemingly endless list of other construction details.

Many designers are apparently ignorant of, or not careful about, some hardware design details. Defects in these areas can make or break a product. I recommend both of these books for those involved in the design of electronic equipment of any type. Even the most successful designers will learn something from them.

While I am more familiar with the Morrison book, I am more impressed with the one by Ott. Interestingly, with so few books available on noise reduction, both texts come from Wiley-Interscience. And although they compete for a position in the marketplace, they also complement one another.

Grounding and Shielding Techniques is a good book for those with a more casual interest in the design of electronics and a main concern with interconnecting systems using good grounding and shielding methods. It is only 172 pages, but it is crammed with information. Its only problem is that it lacks references for further study. To me, this is an important defect since I usually dig deeper when I have a problem and only a partial solution; references make a good starting point. The book is with out doubt based on extensive experience on the part of the author. He has a clear and friendly writing style and explains the figures and his interpretations of systems clearly and accurately. Morrison covers both electrostatic and electromagnetic shielding problems, and he has a nice section on the use of differential inputs for instrumentation purposes.

After three short chapters on electro static principles, the author gets down to the shielding of instruments and does so with considerable specificity.

These chapters include details about shielding power lines, transformers, and the like. A rather long chapter on the differential amplifier used as an instrumentation amplifier follows. It contains a detailed discussion of amplifier configurations mainly of interest for instrumentation use rather than audio applications. Topics include every thing from thermocouple to electrocardiogram uses. A short chapter on shielding bridge-type systems follows.

Magnetic processes are covered, with special emphasis on transformer shielding. The problem of radio frequency interference is discussed rather briefly, with some information on transmission lines, and the book concludes with five pages of rather interesting information about making connection to the earth with buried rods and wires. Although it is not particularly relevant for audio applications, I found this discussion enlightening.

The Ott book is much longer, some 364 pages of text and 50 additional pages of problems and solutions. The problem-and-solution section makes Noise Reduction Techniques attractive as a textbook or for the more serious readers who wish to test their knowledge. There is also a good bibliography at the end of each chapter, al though I found some lack of references from the last half-dozen years. Nevertheless, this is a much more scholarly work and covers a greater variety of topics than does Morrison's.

The material in Ott's book ranges from shielding and cabling to active device noise and digital-circuit shielding. Everything is discussed from a solid theoretical base, and many practical examples are given. Almost all of the topics covered are of great interest to anyone concerned about designing electronic equipment capable of re producing wide dynamic range. This applies especially to modern audio equipment, which is often a combination of analog and digital circuitry.

A brief introductory chapter is followed by two very thorough chapters on cabling and grounding. The analyses and discussions presented should satisfy any needs for information about interconnecting electronic boxes for noise-free operation and about routing he signal between components with out degradation. The material is as complete and clear as any I have seen. The chapter on balanced circuits s a bit short, but this is where Groundng and Shielding Techniques can augment what is presented here. A short chapter on passive components contains some interesting information on capacitors and inductors. (The Morrison book has better detail on the top is of transformers.) There is an excellent chapter on shielding, which will be of interest to all box and chassis de signers. I find the chapter on contact protection somewhat out of place, except for the fact that contacts are a serious noise source in some systems.

Chapters 8 and 9 are on intrinsic and active noise sources. These sections will be of interest principally to circuit designers and are important because they set the ultimate lower noise limit for most equipment. There is an excellent chapter on digital circuit noise and layout, and one on digital radiation. These topics are of great interest for those involved in the design of equipment that is partially digital and partially analog.

I found the final chapter, on electro static discharge, very interesting. It explains why walking around and then touching equipment causes sparks and thus pops and clicks-or worse in electronic equipment.

Noise Reduction Techniques is thorough, accurate, and full of practical discussions. It is one book which should be required reading for every person who wants to be knowledge able about cabling, noise, and interference. I recommend it highly.

Both volumes are so good in their own ways that neither really upstages the other. Ott's book is essential to those who would understand the over all design and interconnection of modern analog/digital electronics. Morrison's is full of practical information about interconnecting equipment, and it offers a clear and very practical discussion of instrumentation techniques.

-R. A. Greiner

R. A. Greiner is Professor in the Department of Electrical and Computer Engineering at the University of Wisconsin in Madison, Wisc.

Total Harmonic Distortion by Charles Rodrigues. Perfectbound Press, 128 pp., paperback, $7.95. (Available only by mail from Perfectbound Press, 1120 Ave. of the Americas, Suite 4118C, New York, N.Y. 10036. Add $1.50 post age and handling per U.S. order; for foreign orders, add $1.75 for the first book and 500 for each additional copy; New York State residents, add 650 sales tax per book.)

Audio and video are Serious Matters; there's nothing funny about them. But the people involved in those fields, both professionally and as customers, are something else again. Charles Rodrigues has been poking fun at them (but not at you and me, of course) in his cartoons in Stereo Review since 1958. Now, 118 of those cartoons have been collected by David Stein, Stereo Review's managing editor, in a paper back all too appropriately entitled Total Harmonic Distortion. Total pandemonium is more like it: Leafing through, you'll get a fresh look at audiophile sympathy cards, viscous-damped turntables, the influence of supertankers on FM reception, how a child prodigy's career ends, what to do if you don't trust your test record, the non-acoustic advantages of pyramidal speakers, and most important of all, how to buy expensive speakers when your spouse is watching.

Why sit there, deluged with useful information, when Charles Rodrigues is so willing to purvey the other kind?

-Ivan Berger

(adapted from Audio magazine, Dec. 1988)

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