digital audio discordance

Emedia Professional, Jan 1, 1999 by Dana J. Parker

At long last--over two-and-a-half years late--the DVD Forum has announced version 1.0 of the DVD-Audio spec--sort of--and it's so wide open you could steer a super tanker through it. True to form, Sony and Philips will be promoting a fundamentally different spec, Super Audio CD (SACD), based on a recording method called DSD (Direct Stream Digital).

In what's become a familiar scenario, the DVD-Audio spec took so long because of the difficulty of reaching consensus in the working group for DVD-Audio, which grew to 39 members in the time it took to arrive at a spec. It's only "sort of" a spec because copy protection issues have not been sorted out yet. It's so inclusive because the DVD Forum apparently decided that the way to discourage alternative formats was to recognize each member's suggestions. This tactic seems to have worked for three out of four proposed DVD-Audio formats. The other members of the DVD Audio Working Group are hoping that Sony and Philips will endorse the Forum's DVD-Audio, and thus avert a format war. Hope, as always, springs eternal.

The DVD-Audio spec includes a mandatory requirement for uncompressed, lossless Linear Pulse Code Modulation (LPCM), plus future "optional" audio signals--perhaps including DSD (Direct Stream Digital), DTS (Digital Theater System), and Dolby AC3 (a.k.a. Dolby Digital)--to be defined after version 1.0." You can record at a sampling rate from 44.1kHz to 192kHz, and in 16, 20, and 24 quantization bits, and in two to six channels. In other words, you can use just about any recording method you want, and you can still call it DVD-Audio. At its most basic level--the one that most manufacturers are likely to build players to--DVD-Audio is a souped-up audio CD, with higher sampling rates, larger sample sizes, and the option of up to six channels surround sound.

SACD, on the other hand, is not just the usual Sony/Philips effort to milk old royalty streams, but is based on a truly revolutionary way of recording sound. DSD is a "scalable" bitstream technology. The signal can be converted to any commonly-used sampling rate and word length (quantization) used in PCM. The same disc could sound OK on a boombox, great on a car stereo system, and absolutely superb in an audiophile's $50,000 home stereo. Better yet, the same disc could play on today's audio CD players, thanks to a specified CD audio layer in addition to a high-density DSD layer. Sony and Philips plan to offer the spec, known as the "Scarlet Book," to existing licensees of the Red Book CD Audio specification, at minimal cost.

SACD is not without its detractors, however. According to one senior electronics engineer, who asked to remain nameless, the most important drawbacks of SACD are that it requires complex, but cheap, Digital-to-Analog converters, indicating that SACD is geared to low-quality mass market gear; the bitstream could be very sensitive to jitter (timing errors); and, as a new audio approach, there are no standard paradigms for processing a DSD/SACD stream digitally in the studio. Standard PCM, by comparison, "has been with us since 1938, and is firmly founded in signal theory." The same engineer credits DVD-Audio with "flexibility of implementation: sampling rates, word-lengths, number of channels ... all are determined in the software, whereas SACD is one rigid specific implementation and no more." And, as Apogee's Richard Elen writes in AudioMedia, converting to DSD recording capabilities means replacing "virtually every piece of recording equipment" in the studio.

BUT WHAT DOES THIS MEAN TO US?

Both formats reportedly sound great. For those blessed with golden ears and knockout home stereos in acoustically ideal environments, the difference in quality could be compelling. For those of us with ten-year-old bookshelf JBLs and plenty of ambient noise in our "listening rooms," the improvement over CDs may not be noticeable. Consumer electronics companies are therefore betting on multi-channel sound and added features--such as liner notes, slideshows, and DVD-Video clips--to entice consumers to upgrade to a higher quality audio format.

Standalone DVD-Audio players are unlikely to appeal to any but audio purists. The most likely scenario is that future DVD-Video players will be modified to accept 24-bit, 96kHz, LPCM DVD-Audio discs. Even though 24/96 is the current audio high-end of the DVD-Video specs, most DVD-Video players are capable of decoding audio only at 20/48. And most consumers--and even some audio professionals--find this not just perfectly adequate, but the best they've ever heard.

Some professional audio pundits say that DSD will appeal to fans of "serious" music, while DVD-Audio's PCM will attract listeners of "popular" music. Others say there's really no demand for a higher-quality digital audio format at all--except in the declining audio industry. The RIAA reports that 1996 was the first year in which CD sales did not increase by double digits, and CD sales actually fell 2.3 percent in the first half of 1997. Audio component sales, according to the Consumer Electronics Manufacturers Association, experienced 13 consecutive months of single and double-digit declines through the first half of 1997.