Digital Processor Reviews

Fifteen years? Has it really been 15 years since I reviewed what was then the flagship D/A processor from English company Chord Electronics? In the July 2002 issue, here's how I summed up my review of the Chord DAC64: "While the Chord Electronics DAC64 is undoubtedly expensive, it is eye-poppingly gorgeous. . . . many listeners should find its silky-smooth highs seductive, as well as its slightly larger-than-life lows." How times and prices change—the "undoubtedly expensive" DAC64 cost only $3040! I did make a couple of criticisms of the DAC64 in my review, but according to Wes Phillips, in his August 2007 review of Chord's revised DAC64, "the Choral Blu [CD transport] and Choral DAC64 are, together, the CD player we music lovers have long prayed for"—even if, five years after my own review, the DAC64's price had risen to $5000.

Now that we've entered a world of post-disc audio (sorry, AnalogPlanet.com), audiophile streaming and file-playback products have appeared by the hundreds, and many companies are on their second, third, or even fourth-generation models.

The Chinese company Auralic Limited has been pushing bits around for seven years, releasing a half-dozen streaming and network devices. Their newest, the Altair, combines in a single package the functions of a DAC, streamer, and headphone amplifier with volume control, allowing it also to operate as an all-digital-system preamplifier. Just add power amp and speakers.

It has been 20 years since I first became aware of the British company Data Conversion Systems, which manufactures audio products under the dCS brand. Rather than use off-the-shelf conversion chips, the groundbreaking dCS Elgar D/A converter, which I reviewed in our July 1997 issue, featured a then-unique D/A design that they called a Ring DAC. This featured a five-bit, unitary-weighted, discrete DAC running at 64 times the incoming data's sample rate—2.822MHz for 44.1kHz-based data, 3.07MHz for 48kHz-sampled data and its multiples—with upsampling and digital filtering and processing implemented in Field Programmable Gate Arrays (FPGAs). Oversampling to a very high sample rate allows the word length to be reduced without losing resolution, and use of a low-bit multi-bit DAC makes for very high accuracy in the analog voltage levels that describe the signal. (If this seems like voodoo, for a given signal bandwidth, bit depth and sample rate are related. To oversimplify, double the rate, and you can reduce the bit depth by one bit while preserving the overall resolution.)