Digital Processor Reviews

At the 2019 AXPONA, I took part in one of my first official meetings, as editor of Stereophile, with members of the manufacturing community: the German company T+A. They were presenting in the room of Texas dealer Lone Star Audio, which was owned by the late Jim Hench. They had a corner hallway to themselves: two rooms and, at the time when I arrived, a hallway table brimming with coffee and pastries. Fortuitous timing.

The idea of using digital signal processing (DSP) to convert digital audio data sampled at 44.1kHz or 48kHz to a higher sample rate is not new. I first heard the beneficial effects of upsampling at Stereophile's 1998 hi-fi show in Los Angeles, where a pro-audio dCS 972 digital-to-digital processor was being used to convert 16-bit/44.1kHz CD data to a 24/192 datastream.

Even as digital/analog processors were becoming a hot product category in the early 1990s, audiophiles were also learning that timing uncertainties in the AES/EBU and S/PDIF serial datastreams—jitter—would compromise any improvement in sound quality offered by these DACs. Some companies therefore introduced products to reduce or eliminate jitter—in the November 1994 issue of Stereophile, Robert Harley reviewed three such products: the Audio Alchemy DTI Pro, the Digital Domain VSP, and the Sonic Frontiers UltrajitterBug. I still have Stereophile's review samples of the UltraJitterBug and VSP, along with two contemporary DACs: a PS Audio UltraLink and a Parts Connection Assemblage DAC-1.

As our reviews of these products were published before Paul Miller's and the late Julian Dunn's development of the "J-Test" diagnostic signal, I performed J-Test jitter measurements to bring that 1994 review into the 21st Century. You can see what I found here.

Making digital audio sound good appears to be a much more difficult job than its developers first realized. When digital audio was in its infancy, there was a tendency to think that digital either worked perfectly, or didn't work at all. This belief led the engineering community to devise ill-considered and flawed standards that affect the musical quality of digitally reproduced music today.

As the sides of the slim-line Timbre Technology TT-1 DAC are radiused rather than flat, it's elegant compared to its typical boxy competition. While the TT-1's handsome shape stands out more than your average audiophile device, its curved sides help create a stronger, less resonant shape than the usual box, and serve as just one of the many elements contributing to a high degree of mechanical integrity and damping.

This is the 100th and—surprise!—final edition of Music in the Round. MitR began in mid-2003, shortly after SACD and DVD-A discs made high-quality multichannel music convenient and widely available. At the time, I was convinced that multichannel reproduction was superior to stereo because it was able to reproduce the full sound of the performance—not just the performers. Stereophile's founder, J. Gordon Holt, had promoted this idea many times, but the appearance of the new media finally brought it to a wider audience.

The $799 Theorem was originally shown at the 1992 WCES in a very small chassis that prohibited adding features or upgrades. Sumo has since become more ambitious, putting the Theorem in a full-sized chassis and offering several upgrade options that would have been impossible in the truncated version.