Reference

The Complete Guide to High-End Audio
by Robert Harley
450+xxiv pp., $29.95 softcover, $39.95 signed hardcover. Published by Acapella Publishing, P.O. Box 80805, Albuquerque, NM 87198-0805. Credit-card orders: (800) 848-5099.

In the October 1994 Stereophile (Vol.17 No.10, p.39), I discussed my experiences with the DTS audio data-reduction code/decode switch box, which, briefly, is a two-channel box that makes use of the algorithm DTS has proposed for their version of discrete multichannel sound for laserdiscs.

Anyone who's ever looked for it knows how rare audio-friendly living space is. Perhaps someday an enterprising developer will build Audiophile Acres---a whole subdivision of audio houses or soundproofed condos that'll meet these needs---then stand by while hordes of long-suffering audiophiles stampede the sales office, frantically waving down-payments in their sweaty hands.

On a number of occasions we have commented on the effects of an amplifier's output impedance on a system's performance. A high output impedance—such as is found in many tube amplifiers—will interact with the loudspeaker's impedance in a way which directly affects the combination's frequency response. The Cary">http://www.stereophile.com//amplificationreviews/740/">Cary CAD-805, for example, has a lower output impedance than most tube amplifiers, and should be less prone to such interaction. Some months back—before the CAD-805 arrived—I investigated this phenomenon in conjunction with measurements for a forthcoming review of the Melos 400 monoblock amplifier. Since the Melos 400 also had a relatively low output impedance for a tube amplifier (at 0.43 ohms at low and mid frequencies, rising to 1.2 ohms at 20kHz, from its 8 ohm tap), I took that opportunity to run some frequency-response measurements using an actual loudspeaker as the load for the amplifier.

Until recently, all problems in digital audio systems were blamed on either the analog/digital converters (ADCs) used in mastering or the digital/analog converters (DACs) needed for playback (footnote 1). As the performance of both ADCs and DACs improved, however, a previously unrecognized mechanism for distortion was unmasked: jitter. As we shall see, jitter—or, more correctly, word-clock jitter—can be a significant limitation in the technical and sonic performance of digital audio systems (footnote 2).

Though we sometimes take for granted that the basic "language" of our measurements is clear to all of our readers, letters to the editor tell us that this is not the case. Periodically, then, we will attempt to explain exactly what our measurements are and what they purport to show. Though those with technical training may find our explanations a bit simplistic, they're aimed at the reader who lacks such experience.

I recently scoured my shelves and came up with the following list of must-read books for stereophiles, all of which are in print and should be available from specialist bookshops or from the suppliers mentioned in the text. Books marked with an asterisk (*), though too technical for the general reader, will be found rewarding by those who have a good grasp of mathematics and who want to delve deep. Reading the books in the first "general" section of the list will enable readers to understand just about everything that appears in Stereophile, but all the books listed contain between their covers untold treasures.