Digital Processor Reviews

John Stronczer, Bel Canto Design's technical spark plug, meets my definition of an electronics renaissance man, ranging as he does from designing single-ended amps that glow in the dark (the Orfeo) to digital processors (the Aida). Actually, digital circuitry is one of John's specialties, dating back to his days at Honeywell.

If there's one buzzword in high-end audio for the 1990s, it's undoubtedly jitter. "Jitter" describes timing variations in the clock controlling the ones and zeros that represent the analog audio signal. If that clock isn't stable to an extraordinarily precise degree, the sound quality of the digital processor will be degraded.

A CD transport/digital processor combination introduces jitter in three ways: 1) the transport puts out a jittered signal; 2) the S/PDIF or AES/EBU interface between the transport and processor creates jitter; and 3) the digital processor adds its own jitter to the clock. These additive factors are largely responsible for the great range in sound quality we hear from different transports and interfaces.

The arrival of the Mark">http://www.stereophile.com/digitalprocessors/mark_levinson_no30_referen… Levinson No.30 digital processor more than 2½ years ago marked a turning point in digital-audio reproduction. Although the No.30's $13,950 price tag put it out of reach of all but a few audiophiles, its stunning performance suggested that much more musical information was encoded on our CDs, waiting to be recovered by better digital processors. Further, it was inevitable that this level of performance would become less expensive over time. I was more excited by the No.30 than I've been over any other audio product. In fact, its musical performance was so spectacular that it alone occupied the Class A category in Stereophile's "Recommended Components."

Remember the early days of CD, when some players were touted as having the revolutionary new "2x-oversampling" digital filters?

I feel privileged to have followed the remarkable evolution of digital processors over the past four-and-a-half years. Since my first digital review—a survey of three modified CD players back in August 1989—I've been fascinated by the developments that have inexorably improved the quality of digitally reproduced music.

Whoever invented the adage "Good things come in small packages" wasn't into high-end audio. Most high-end products are huge and heavy, with massive power supplies, thick front panels, and battleship build quality. This dreadnought approach is justified if it directly affects the unit's sonic performance (as in the Mark Levinson No.31 transport, for example). In some products, however, the massive build can reflect a shotgun, overkill approach by the designer, or a mere fashion statement.

There are as many ways of designing a digital-to-analog converter as there are engineers. One approach is to select parts from manufacturers' data books and build the product according to the "application notes" provided by the parts manufacturers. This is the electronic equivalent of a paint-by-numbers kit.

A more creative engineer may add a few tricks of his own to the standard brew. Bigger and better regulated power supplies, careful circuit-board layout, tweaky passive components, and attention to detail will likely make this designer's product sound better than the same basic building blocks implemented without this care. Indeed, the vast range of sonic flavors from digital processors containing very nearly the same parts attests to the designer's influence over a digital processor's sound.