The AAC (Advanced Audio Codec), the audio format supported by Apple's iTunes Music Store, has been chosen as a key future DVD Audio disc technology by the standard's governing body, the DVD Forum.
According to an unnamed Forum member cited by web site High Fidelity Review, AAC beat Microsoft's Windows Media 9 format, MP3 and Sony's ATRAC because it "sounded better than the others".
Ironically, the Forum recently selected Windows Media as the basis for its future high-definition video DVD format.
First launched in the late 1990s, DVD Audio is being pitched as a successor to the CD. Sony and Philips are similarly promoting their own next-generation audio format, Super Audio CD (SACD). Keen to avoid the freedom the CD format has granted to PC users to rip tracks to compressed audio formats, DVD Audio was always intended to feature copy protection, though initial versions of the specification lack this 'feature' in order to allow manufacturers to bring players to market.
In order to ensure DVD Audio playback on personal computers, the DVD Forum has proposed the inclusion of a DVD-ROM 'zone' on each DVD Audio disc, which the PC-based player will read in preference to the main audio area. That DVD-ROM will hold compressed versions of the songs encoded in DVD Audio format, and its for these compressed tracks that AAC has now been chosen.
In addition to its superior sound quality, the format was selected for its support for both multi-channel audio and DRM. Apple uses the latter to protect tracks bought from ITMS. AAC doesn't inherently feature DRM, but its file structure was devised to allow the addition of DRM-related control data.
Just as DRM is optional within the AAC file, so too is the DVD-ROM zone within the DVD Audio disc. However, the fact that it is there as a choice for music labels to use should encourage more portable music player makers to build AAC support into their devices as Apple has with its iPod. AAC is also part of the MPEG 4 specification.
DVD Audio provides music encoded in multi-channel format, such as Dolby 5.1, or as high-resolution stereo. The latter digitises sound in 24-bit blocks at up to 192kHz, compared to CD's 16-bit quantisation and 44kHz sample rate. With a single-layer disc, that's enough for two hours' high-res stereo, rising to over three-and-a-half hours' playback with a dual-layer disc. ®