Digital Memory Lane

The January 2021 issue’s cover story on the remarkable Wadax Reference DAC prompted me to look back at the evolution of digital audio since the Compact Disc’s introduction in 1982, and to consider just how far we’ve come. 

The standards for the CD format, a 44.1kHz sample rate and 16-bit quantization, were established in the late 1970s, the Pleistocene era in digital audio. Although a higher sample rate and longer word length would have been better, we’re lucky that Sony and Philips didn’t settle on 32kHz sampling and 14-bit quantization, specifications that were seriously considered. In fact, Philips had manufactured 14-bit DAC chips in anticipation of 14-bit CD, and ended up using these 14-bit parts in its first players. Many of us decried the CD’s fundamental specs as being inadequate, but it turns out that the format, when implemented with today’s best technology and practices, can sound superb. It just took the great talents of inspired high-end designers working tirelessly for nearly four decades to get there.

Almost immediately after CD’s introduction, high-end designers set about improving the format. Their first efforts were modified mass-market CD players because it was impossible to source the chips and drive mechanisms. Modifications usually involved replacing the cheap op-amp-based analog output stage with a discrete circuit, power supply upgrades, improved wiring, and better shielding. After the Meridian MCD Pro in 1984 (the first “audiophile” CD player), the go-to player for music lovers wanting better CD sound was the California Audio Labs Tempest ($1895 in 1986). The Tempest, designed by Mike Moffat (later of Theta and now with Schiit Audio), was a Magnavox player with Moffat’s tube output stage. It was the precursor to a long history of innovation, both by Moffat and the industry in general.

The advent of separate transports and DACs was the catalyst for an explosion of creativity from the high end. With the ability to buy input receivers, digital filters, and DAC chips, high-end designers began to apply a musically sensitive approach to digital audio reproduction. In those early days, many phenomena that affected sound quality were still a mystery. Designers relied on their ears to guide development, discovering techniques for extracting greater musical performance from the new digital medium. Some manufacturers, dissatisfied with the off-the-shelf digital filters, wrote their own filter software to run on general-purpose DSP chips, an approach pioneered by Wadia, Theta, and Krell beginning in 1989. It turned out that the specific filtering approach greatly influenced sound quality, which is why each of those brands had a distinctive sound. 

In 1989, a company called UltraAnalog created a very expensive ($250 each in quantity) DAC module that virtually eliminated linearity errors—the bane of 1980s and early 1990s ladder DAC chips. The UltraAnalog DACs became the standard in high-end converters. A landmark product that showcased the UltraAnalog DAC was the Mark Levinson No.30, the most ambitious effort at the time. It sold for $13,950 in 1992, and was hugely successful. The Spectral SDR-2000 ($8195 in 1995) was another milestone converter using UltraAnalog DACs that revealed digital audio’s potential. High-Definition Compatible Digital (HDCD), an encode-decode technology introduced in the early 1990s and used in the Spectral DAC, employed clever tricks to extract more performance from the CD format.

Off-the-shelf digital filters improved greatly in the late 1990s and early 2000s, and new DAC-chip architectures appeared that overcame limitations of early conversion technology. Data Conversion Systems (dCS) of England developed its innovative “Ring DAC” that greatly reduced low-level linearity errors. DAC-chip manufacturers began to improve their devices, while also including more and more functions in a single chip. Today’s DAC chips incorporate sophisticated digital filtering and upsampling, can decode high-res PCM and DSD, and reject incoming jitter.

Concurrently, the recording industry was adopting high-resolution recording, which, with careful mastering techniques, could yield significant improvements when down-converted to 44.1kHz/16-bit formats. The obvious next step was a new format that could deliver high-resolution to consumers. The roadblocks were both political and technical. Record companies didn’t want to release master-quality recordings that were susceptible to file-sharing, and there was no consumer format for carrying high-res. The DVD-Audio format provided the technical solution, but it never caught on among audiophiles. The competing Super Audio Compact Disc (SACD) was more successful, but remains a niche format today.

The Internet obviated the need for physical formats. Today, we can stream high-resolution, whether Qobuz or Tidal MQA. These high-res bitstreams are turned back into music with DACs that represent decades of hard-won knowledge acquired through the tireless efforts of high-end designers. The Wadax Reference DAC, with its highly sophisticated technology and extraordinary execution, is the pinnacle of this evolution. It serves as a reminder of just how far digital audio has progressed in our lifetimes.