Resolution advances aren’t just part of the HDTV picture. The additional disc capacity provided by Blu-ray and HD DVD allow for expanded audio, too, and Dolby and DTS have ramped up surround-sound offerings to make use of the extra bandwidth. Here’s a peek at the latest high-res audio codecs.

DTS-HD Master Audio
No compression is used in DTS-HD Master Audio, which delivers up to 7.1 channels of lossless sound with 96/24 resolution (that’s a sampling rate of 96,000 times per second compared with 48,000 for standard DVD, and bit depth of 24 versus 16 for CD). The soundtrack is identical to the original, so you lose nothing on playback. If the audio is decoded in a Blu-ray or HD DVD player, it will output as a linear PCM stream, which can run over HDMI 1.1 or 1.2. If the decoder is in the A/V receiver, on the other hand, you’ll need an HDMI 1.3 connection. Currently there are no players or receivers that support HD Master Audio, but DTS expects products to begin rolling out later this year.

DTS-HD High-Resolution Audio
On discs with limited space, studios may choose a slightly compressed version of 96/24 audio called DTS-HD High-Resolution. Where does the compression occur? “Usually when there is a lot of harmonic complexity in the soundtrack, such as voicings and sound effects—and with heavy use of rear-channel information,” says Tom Dixon, director of strategic marketing at DTS. “Higher sampling frequencies, greater bit depth and additional channels also contribute to higher-peak bit rates.” DTS-HD High-Resolution can pass through HDMI 1.1 and 1.2.

Dolby TrueHD
Dolby TrueHD is also a lossless, no-compression 96/24 audio technology for Blu-ray and HD DVD that’s bit for bit identical to the studio master recording. It is the mandatory surround-sound format for HD DVD and is optional for Blu-ray. Among the current crop of high-def players, the Sony PlayStation 3 decodes TrueHD to PCM audio and outputs the signal via HDMI.

Dolby Digital Plus
Dolby Digital Plus is Dolby’s efficient codec for next-generation disc formats. According to Craig Eggers, senior manager of consumer electronics partner marketing for Dolby, “When a movie demands a lot of data for the high-definition video performance, Dolby Digital Plus can offer high-resolution multichannel audio without impacting production bit demands for high-quality video, content extras, and so on.”

Currently, players with built-in Dolby Digital Plus decoders include LG’s BD100 dual-format player, Toshiba’s HD-XA2 and HD-A2 HD DVD players, Panasonic’s DMP-BD10K Blu-ray Disc player and Samsung’s BD-P1200 Blu-ray Disc player. In addition, Dolby expects Sony and Onkyo audio/video receivers due out later this year to incorporate Dolby TrueHD and Dolby Digital Plus. According to Eggers, consumers will get the most out of Dolby Digital Plus via an HDMI connection to the receiver, but they can also use analog or digital connections.

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