Articles and whitepapers

18/6/2003

What is DVD-Audio (DVD-A)?

By Richard Elen

DVD-Audio (DVD-A) takes the DVD-Video disc - the most popular consumer electronics product ever - and extends it to offer the highest-quality stereo and surround audio. Employing high sample rates, up to 192kHz, and word lengths of up to 24 bits, DVD-A discs are compatible with the millions of DVD-Video players already in consumers' homes, while delivering very high performance from DVD-Audio-capable DVD players.

Whatever format they are released in, the vast majority of today's recordings are made on high-resolution PCM (Pulse Code Modulation) digital workstations, and played back via players or processors that use PCM for their internal digital signal processing. DVD-Audio allows these recordings to be experienced by listeners at home exactly as they were in the recording studio when the final master was played back and the producer said, "That's the one!" By using tried and tested PCM, DVD-Audio offers a clear, transparent link between the artist and producer on the one hand, and the record buyer on the other - without complex standards conversion or artefacts either in the studio or in the replay system at home. Supported by four out of five of the leading record companies in the world and literally scores of smaller labels, as well as the vast majority of hardware manufacturers, DVD-Audio is already a popular medium for the distribution of highest-quality multichannel audio to the listening public, and its popularity is growing rapidly.

Superb Sound Quality - and Surround

When new high-capacity optical disc-based storage media were originally developed, the obvious application was for the distribution of movies and other visual material. In addition, DVD-Video offers multichannel sound to convey added realism and powerful cinematic sound effects. The international recording industry was also interested in the DVD disc for audio, and when they came to consider the development of a successor to the existing Compact Disc (CD) they had some specific requirements. Most important of all was the provision of multichannel sound at high sample rates, without the 'lossy' compression used on DVD-Video discs (where theoretically inaudible information is removed to save space), and with a longer playing time than the average CD.

To deliver this requirement, Meridian Lossless Packing (MLP) was developed to compress high-resolution digital audio without losing a single bit of data. The system is so efficient that the data played back from a DVD-Audio disc is bit-for-bit identical to the information that went in, with no loss or compromise. MLP allows the DVD-Audio disc to offer, for a single-layer, single-sided disc, over 80 minutes playing time for six channels of 96kHz, 24-bit digital audio, or two hours of two channels of 192kHz, 24-bit. And it is possible to make discs with two sides, each with two layers. DVD-A can in fact make use of a wide range of sample rates and numbers of channels: you can, for example, deliver 25 hours of CD-quality mono sound from a single layer in the case of a talking book. There is enough space on a DVD-Audio disc to offer multiple audio programmes, for example offering alternate surround mixes and both stereo and surround versions. In addition, DVD-A supports hierarchical multichannel encoding schemes, allowing the format to carry future surround-sound techniques that have yet to be defined.

DVD-Audio/Video Compatibility

The Digital Versatile Disk (DVD) is the most popular consumer electronics product in history. And virtually all DVD-Audio discs can be played back on any of the existing 100 million or so DVD-Video players. The DVD-Video-compatible area on almost every DVD-Audio disc means that no special equipment is required to enjoy surround sound from a DVD-Audio disc, albeit at DVD-Video quality. At the same time, an increasing number of DVD players include the ability to replay DVD-Audio discs at their highest levels of resolution, and it is likely that almost every new player will be DVD-A compatible. DVD-A playback capability is also available for computer systems and for use in cars and other environments.

Added Value - ROM and Visual Material As DVD-Audio is part of the DVD 'family', it inherits all the capabilities of the DVD-Video disc and includes some additional ones of its own. The DVD-Video area of the disc can include all the features of a standard DVD-V disc, including full-motion, high-resolution video, DTS or Dolby stereo or surround soundtracks, and more.

Choice of full motion video, multichannel and stereo audio in the
DVD-Video area of the disc

The DVD-A area, in addition to superb quality audio, can carry still images, which can be shown sequentially as a slideshow, along with lyric sheets and other data such as artist commentaries. Access to all these features is via a comprehensive menu system that will be familiar to DVD-Video users.

Choice of multichannel audio, stereo and stills in the
DVD-Audio area of the disc

You can also simply insert a disc and press Play to play the audio content in the same way as a conventional CD. Finally, a DVD-ROM area on the disc can be used to store additional materials for access via a computer.

Content Protection

One of the primary requirements of the ISC, the industry body overseeing the development of the new high-resolution music carrier, was the inclusion of robust methods of protecting intellectual property, both from 'ripping' content to other media such as on-line file sharing, and from concerted attempts to clone and 'pirate' the discs themselves. As a result, DVD-A was developed to include a multi-part security system. Strong encryption prevents 'ripping' of the content in such a sophisticated fashion that even if one of the millions of 'keys' is cracked, that key can be invalidated after the event. Optional watermarking enables illegal copying to be detected, even in analogue copies, while a detector in the player will eject a pirated disc.

Richard Elen provides Creative Services for Meridian Audio Ltd.

Telephone 01480 445678
www.meridian-audio.com

For more details on developments in DVD-Audio, visit
www.dvdaudio-info.com