DVD Working Group 4 to release DVD-Audio specification in May

The DVD Forum's Working Group 4 (WG-4) is expected to deliver the "0.9" version of its official DVD-Audio specification this month, with "1.0" to follow shortly. While information is scarce, it appears that WG-4 is talking about four different kinds of disc, each of which will be playable on one or two of three different kinds of players. And that doesn't include Sony's and Philips' "Super Audio CD" proposal (see Peter van Willenswaard's report on SACD a couple of weeks back on the website), or the Classic Records-led "DAD" format, which uses the provision of the DVD-Video specification for 24-bit/96kHz audio data. (DADs will play on DVD-Video players that have appropriate D/A sections---also see the past item on the web site.)

The WG-4 proposal is that there be two kinds of DVD-Audio disc: one with additional video content (an AV-Disc) and one without (though the pure audio A-Disc can have optional still pictures and text information); and two kinds of DVD-Video disc: the pure-video V-Disc and what's termed a VAN-Disc. (VAN stands for Video+Audio Navigation, which will enable a pure DVD-Audio player to play the video disc's audio content if permitted by the copyright owner.)

The three different players are a pure video player that will play only DVD-Video discs, a pure audio player that will play DVD-Audio discs and the audio content of VAN-Discs, and a universal player that will play all DVDs. To add to the confusion, while all DVD players are expected to be able to play CDs, the existing universe of CD players will not play WG-4 DVD-Audio discs, but will be able to play the Sony/Philips SACDs.

According to industry newsletter Audio Week, the DVD Forum estimates that the potential exists for 1.5 million DVD-Audio players to be sold in the US in 1999, as well as 10 million DVD-Video players (half of which will be able to play DVD-Audio discs), and the millions of DVD-equipped computers that will be sold in 1999.

The DVD-Audio specification is complex, appearing to cover all possible bases with respect to audio content: scalable linear-PCM, multichannel content with 48kHz/96kHz and 44.4kHz/88.2kHz sample-rate options, 16-/20-/24-bit quantization, and up to six channels of audio data. (The sample rate and quantization can be independently set for each channel.) Producers can provide on-the-fly mixdown instructions so that those with stereo systems or low-cost two-channel DVD-Audio players can still access the multichannel data. Optional data-reduced tracks---Dolby Digital, MPEG-1 and 2, DTS, and SDDS are all mentioned in the spec, I believe---can be included. And, at the WG-4 presentation at last September's Audio Engineering Society Convention, it was confirmed that the specification will be sufficiently flexible to allow for Sony's DSD coding, for lossless compression of high-bit-rate data, and for the 192kHz sample rate proposed by Samsung and dCS.

Both 120mm (4.5") and 80mm (3") DVD-Audio discs can be made. Other than disc size, the only restraint on the disc's contents is that the maximum bit rate for data retrieval not exceed 9.216Mb/s. This is higher than the DVD-Video's 6.4Mb/s, but is still not high enough to allow for 5.1 channels of 24/96 data. However, the maximum data rate does allow three channels of 24/96 data and three channels of 16/48 data to be played back simultaneously, with a maximum playing time for a 120mm single-layer disc of 64 minutes (117 minutes for a dual-layer disc).

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