Digital Processor Reviews

It's common knowledge that manufacturers tune the sound of each DAC model. There are the facts of product design and marketing: inputs, outputs, case materials, price points. After that, what's left are the trade-offs of different circuit designs and filter options, which are chosen with care—each has a subtle yet telling effect on a DAC's sound. Most designers try to go from bits to analog with minimal deviation from perfect. But when you look at the measurements and listen closely, you realize that perfect is elusive. One has to make choices.

Back in the late 1980s, it seemed a good idea: Separate a CD player's transport section from its D/A circuitry so that each could be optimally designed, and, as D/A technology improved, the sound of your CD player could be upgraded by replacing the outboard D/A processor. The catch was that the transport and D/A chassis needed to be connected with a serial data link: S/PDIF in optical or electrical flavors, or balanced AES/EBU. To minimize the number of cables required, the format of that link embedded the clock data within the audio data, which rendered the link sensitive to interface timing uncertainty, or jitter. (See "Bits Is Bits?," by Malcolm Hawksford and Chris Dunn.)

Sure, Stereophile gets letters to the editor. We also get some colorful responses for our "Manufacturers' Comments" section. (Vince Bruzzese and Roy Hall are literary standouts among their component-making peers.) And, as one of the magazine's Contributing Editors (Audio), I get lots of personal mail from readers seeking my advice. I thought I might share some of these letters with you, and my responses.