Digital Processor Reviews

I was setting up for some musical demonstrations I was to present for a Music Matters evening at the ListenUp! store in Boulder, Colorado, in May 2011. For these events, an audio store invites manufacturers (and the occasional journalist) to demonstrate to local audiophiles the musical benefits of high-end audio playback. In Boulder, I was to share the store's big listening room with Dave Nauber, president of Classé Audio, who had set up a system with B&W Diamond 802 speakers, a Classé stereo amplifier, and a preproduction sample of Classé's new CP-800 preamplifier ($5000), all hooked up with AudioQuest cable. I unpacked my MacBook, with which I was going to play the high-resolution master files of some of my Stereophile recordings, and looked around for a DAC. There wasn't one.

There's so much uncertainty and confusion surrounding computer audio and high-resolution downloads. Which hi-rez formats will win out? How do you store the downloads you've bought? (Easy. Don't buy them.) How do you access them? Will digital rights management (DRM) cramp your style, or data-storage fees for cloud computing crumple your wallet?

Who wants only a digital-to-analog converter when you can have a DAC with benefits? How about if those benefits also come with some high-resolution attitude?

That's what I pondered while setting up the NAD M51 ($2000). Sure, it's a basic DAC, but it also has extras—like HDMI inputs, remote-controlled volume, a polarity switch, and one of my favorite features on any DAC: a display that tells you which sampling rate the thing is locked to.

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.

When a manufacturer sets out to design and build a product, be it in high-end audio or any other field, the final retail price is usually a prime consideration. Parts and assembly are only part of the equation; there also must be enough buyers to amortize the design and development costs. If the product is to be a flagship model—something a company hopes will give a lift to its entire line—engineers will sometimes throw caution to the winds, designing a product without thought to its ultimate price, which is only set after the design is complete. When Madrigal Audio Laboratories set out to design their No.30 Reference Digital Processor, they appear to have chosen exactly this approach.

The taxonomy of audio products used to be easy. An amp, a preamp, speakers, a disc player or two—done. Now that hard drives, streaming clouds, and computers have entered the scene, unless your world revolves around only an iPod or a disc player, you have choices—lots of 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.)