Special Coverage: HD DVD

The Sound Also Rises

By Robert Harley

HD DVD offers not just a high-definition picture, but high-definition sound as well. These discs carry new surround-sound audio formats that deliver significantly improved audio quality compared with Dolby Digital and DTS. This development is made possible by the vastly greater storage capacity of HD DVD and Blu-ray, which means less severe compression of the soundtrack. It's thrilling for those of us with high-quality home-theater audio systems.

The new Dolby formats are Dolby Digital Plus and Dolby TrueHD. Dolby Digital Plus is an extension of the conventional Dolby Digital we've been listening to for years on DVD and HD television shows. Dolby Digital Plus offers more channels and a higher bit rate for better sound quality. Where Dolby Digital was limited to a maximum bit rate of 640kbps (384 or 448kbps in practice), Dolby Digital Plus allows scalable bit rates up to 3Mbps on HD DVD and up to 6Mbps on Blu-ray. In addition to more bits per second, Dolby improved the encoding algorithms in Dolby Digital Plus for better sound.

For the ultimate in sound quality, Dolby has introduced Dolby TrueHD, which delivers high-resolution multichannel audio with perfect bit-for-bit accuracy to the source. With TrueHD, you will hear in your home sound quality identical to what the engineers heard in the studio. TrueHD decoding is an option, rather than a requirement, on HD DVD and Blu-ray players. The first title to be released with a Dolby TrueHD track is The Phantom of the Opera. I expect Dolby TrueHD will become standard on musical performances and concert discs.

With more than 40 million Dolby Digital decoders in use throughout the world, Dolby made sure the new formats were backward-compatible with your receiver or controller. The new players output a conventional Dolby Digital or DTS bitstream on the familiar coaxial or optical digital outputs for connection to your receiver. This output will likely sound a little better than Dolby Digital from DVD because it always operates at the highest possible data rate of 640kbps.

But you won't hear the full potential of Dolby Digital Plus or Dolby TrueHD through the coaxial or optical digital output. To hear the new formats' improved sound, you'll need an HD DVD or Blu-ray player with a multichannel analog output, along with a receiver that offers a multichannel analog input. Eventually, Dolby Digital Plus and TrueHD connections will be made via the HDMI 1.3 interface. Until that option is available (perhaps later this year), Dolby Digital Plus and TrueHD decoding will take place in the player and require six or eight analog cables between the player and receiver. For a more detailed explanation of how the players will connect to your existing receiver, see Dolby's white paper on the subject.

DTS has introduced its own high-resolution surround-sound audio formats for HD DVD and Blu-ray called DTS-HD. This new format is an extension of conventional DTS, offering scalable bit rates all the way from 754kbps to 3Mbps on HD DVD and 6Mbps on Blu-ray. A variant of DTS-HD, called DTS-HD Master Audio, can operate at even higher bit rates (up to 18Mbps on HD DVD and 24Mbps on Blu-ray) for true lossless encoding of high-resolution multichannel audio. The "Master Audio" tag signifies lossless encoding. As with Dolby TrueHD, HD DVD players are not required to implement DTS-HD Master Audio; however, if a player encounters that format on a disc, it must at least deliver the DTS core audio stream (that is, good old standard DTS).

The bottom line is that movies and concert performances are about to sound a whole lot better thanks to these advanced new audio formats. We'll have a full report on how Dolby Digital Plus, Dolby TrueHD, DTS-HD, and DTS-HD Master Audio sound in an upcoming issue.

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