stop, hey, what's that sound

Emedia Professional, Jan, 1999 by Jeff Partyka

THE DVD - AUDIO AGE APPROACHES

imagine it's June 2007. You've just come home from the local music store with the newly released DVD-Audio disc of your favorite album, the Beatles' Sgt. Pepper's Lonely Hearts Club Band.

A red label on the plastic wrapper reads, "40th Anniversary DVD Edition--Remastered for Six-Channel Surround Sound."

You fire up your home theater system. You remove your Raiders of the Lost Ark DVD-Video disc from the universal DVD player and in goes Pepper. The ambient orchestra and crowd noises that open the album surround you from at least two directions, and for the first time really make you feel like you're there in the concert hall, waiting for Sgt. Pepper's band to appear.

The drums and bass kick in powerfully from the left and right channels, the lead guitar roars out from somewhere behind you, and then Paul McCartney's voice takes its place center stage--or rather in the center channel: "It was twenty years ago today ..."

Is this the future of audio as promised by the approach of the DVD-Audio age, or is it some audiophile's pipe dream? There's the potential, at least, that it's the former. Multichannel surround sound to replace stereo, longer playing times, improved sound quality, video and textual content in addition to the music--all appear to be very real possibilities for DVD-Audio.

Version 1.0 of the long-awaited DVD-Audio specification is on the horizon (it wax due to be finalized and released by the time this magazine reached your hands), which means manufacture and availability of DVD-Audio hardware is one step closer. Working Group 4 (WG-4), a committee created by the DVD Forum in December 1995 to come up with the spec, issued a draft specification early in 1998 that outlined the technological details and acknowledged the need for music professionals such as artists and producers to join in the effort to make DVD-Audio a reality.

AT LONG LAST, THE SPECIFICATION

The technical leaps from the compact disc to DVD-Audio hold plenty of possibility. While 650-680MB Red Book CDs deliver almost 80 minutes of music in either mono or stereo at a sampling rate of 44.1kHz (44,100 times per second), DVD-Audio can offer longer playing times and multiple-channel sound at 96kHz. DVD's 4.7GB of information per data layer provides plenty of room on a DVD-Audio disc for the higher sampling rates--and consequently improved sound quality.

The DVD-Audio specification derives partly from DVD-Video's audio features. (But that doesn't mean current DVD-Video players will necessarily be able to read DVD-Audio discs; manufacturing plans for the future call for three types of DVD players, including today's DVD-Video players, audio-specific units, and "universal" models that will play both.)

The two formats share linear pulse-code modulation (LPCM) coding, which allows lossless, uncompressed 16-, 20-, or 24-bit PCM audio at a sampling frequency of either 48kHz or 96kHz. Up to eight PCM channels are supported, hut only if the combined bit stream rate is lees than or equal to 9.6MB/sec. Super High Quality Linear PCM, another basic parameter of the format, supports sampling frequencies up to 192kHz, hut only for two-channel stereo sound.

Despite the technical potential for eight-channel reproduction, don't expect "octophonic" recordings of your favorite albums to start hitting the shelves. The spec also incorporates Meridian Lossless Packing (MLP)--the compression technology embraced by the WG-4 and included in the DVD-Audio spec--which means six will actually be the magic number. "Six channels of 96kHz, 24-hit sound can be put on the disc using MLP--otherwise the bit rate for DVD would he exceeded," says Jordan Rost, senior vice president of new technologies at Warner Music Group and a member of WG-4. "The current 74-minute standard in CDs can now he accommodated with DVD-Audio with an exact bit-for-bit reproduction of 96/24 masters."

Dolby Labs, which had advised the Working Group that a single data layer on a DVD disc could accommodate 95 minutes of 5.1-channel 96/24 PCM audio, ended up agreeing to license MLP on behalf of its developer, Meridian Audi. According to WG-4, tests indicated that MLP could squeeze between 77 and 133 minutes of six-channel PCM audio without any loss of audio data. MLP could also pack 122 to 136 minutes of 192kHz, 24-hit Super High Quality LPCM stereo sound onto a data layer, conceivably for audiophile-quality archiving of older mono and stereo recordings.

The warmer, more natural sound quality and the multichannel capabilities made possible by the accommodation of more musical information in the DVD-Audio spec will most likely prove the key selling points of the new format. "We do know that sound quality is a very important issue to consumers, and that multichannel sound is a very important and popular aspect of DVD-Video," says Rost. "In addition, added-value content can be included on the disc like a music video clip, discography, video liner notes, and easy connection to the artist's Internet site."