The Evolution of Surround Sound: Dolby vs DTS
Believe it or not, there was a time when surround sound was a novelty. Here's a look back at its origin, advances and latest hi-def formats.
Dolby vs DTS
April 08, 2008 by Dennis P. Barker

Dolby Digital Plus was specifically designed for high definition discs such as HD DVD and Blu-ray Disc. It employs an altogether new technique to address the downmix compatibility issue, and is the only perceptual coder thus far to do so. In its “core plus extension” structure, the Dolby Digital Plus core is a complete 5.1-channel mix; the extension contains the new channels, plus any channels that have been modified between the 5.1 and 7.1 renditions. The high coding efficiency of Dolby Digital Plus—coupled with the large capacity of HD disc formats—means there is no material penalty in employing this method. Dolby Digital Plus can deliver 7.1channel soundtracks with superb quality at bit rates of 1 Mbps or less. No longer restricted to 448 kbps, Dolby Digital Plus—and Dolby Digital—will bring enhanced quality from a highly sophisticated perceptual audio coder while concurrently enabling content providers to include multiple surround audio streams on the disc without impacting the data needed for high-quality video or added feature content.

Dolby TrueHD
Dolby TrueHD is the pinnacle of Dolby’s next-generation lossless technology developed for high-definition disc-based media. Dolby TrueHD delivers tantalizing sound that is bit-for-bit identical to the studio master, unlocking the true high-definition entertainment experience on next-generation discs. When coupled with high-definition video, Dolby TrueHD offers an unprecedented home theater experience that lets you enjoy sound as stunning as the high-definition picture. It features: 100 percent lossless coding technology, up to 18 Mbps bit rate, supports up to eight full-range channels of 24-bit/96 kHz audio supported by High-Definition Media Interface (HDMI), supports extensive metadata including dialogue normalization and dynamic range control.

From its inception, Dolby Digital was not bound to any prior channel extension methodology, and could therefore benefit from the subsequent developments of other multichannel codecs. One example of a channel extension technique is the method by which MLP Lossless, Dolby TrueHD, and MPEG-2 LII deliver compatible downmixes for soundtracks with expanded channels. In these codecs, a 7.1-channel soundtrack is first downmixed to create a 5.1 mix, which is supplemented by a two-channel extension (which we’ll call “extension B”). The 5.1 mix is then further downmixed to a two-channel stereo mix, and another supplemental stream is created that carries the 3.1-channel “extension A.” So the 7.1-channel program is delivered in three separate components: a two-channel mix, the 3.1-channel extension A, and the two-channel extension B. The total payload is still 7.1 channels, with preconfigured subsets to create two-, 5.1-, and 7.1-channel presentations. Re-matrixing is itself not a problem, and because it works perfectly with MLP Lossless coding on the now defunct DVD-Audio, the method was carried over into Dolby TrueHD. 

The core technology of Dolby TrueHD is MLP Lossless. As a result, MLP has been in use longer and more widely than any other lossless audio technology, proving itself to consumers and industry experts alike. Dolby TrueHD supports double the maximum bit rate (18 Mbps), double the possible number of channels (14.0), more options for stereo support (including delivering a totally separate stereo mix rather than a downmix), the addition of metadata as used in Dolby Digital—including dialogue normalization and dynamic range control—as well as support for all the new channels introduced in SMPTE 428M.  Dolby TrueHD delivers the lossless audio experience demanded by home theater enthusiasts for high-definition video content.

DTS-HD
DTS-HD is obviously DTS’ answer to Dolby Digital Plus. It can encode and decode audio at super high bit rates. In digital recording, the faster the transfer of digital information (data rate), the better the sound quality. DTS-HD has the ability to deliver very high data rates that can capture virtually all of the original audio information (DTS-HD High Resolution Audio) or ALL of the information (DTS-HD Master Audio). What this means is surround sound with unprecedented accuracy and realism.

DTS-HD delivers wider frequency response and greater dynamic range for both movies and music. Higher sampling rates and greater bit depth mean more realistic sounds (clearer and accurate) and greater dynamic punch. Music and dialogue will sound more clear and accurate, and the dynamic range of action sound effects will be dramatically improved. DTS was the only format that delivered 96k/24 bit sound to standard DVD Video discs, and it continues to lead the way in audio performance with Blu-ray and HD-DVD discs.  DTS-HD is capable of 7.1 channels that immerse the listener in a perfect movie or music experience. The additional channels radiate uniform sound coverage throughout your living room, virtually eliminating any “holes” in the surround sound field. It delivers a fully immersive surround experience for everyone in the room - and not just for the person sitting in the “sweet spot.” Many 2008 A/V receivers now include a DTS-HD decoder built-in At the same time, several Blu-ray Disc players may also include a DTS-HD decoder built-in. The new player can connect to your existing receiver with a S/PDIF or HDMI digital input, or 7.1 channel analog inputs.

DTS HD Master Audio
DTS-HD Master Audio is capable of delivering audio that is a bit-for-bit identical to the studio master, and is on par with Dolby True HD. With DTS-HD Master Audio the listener will reportedly experience movies and music exactly as the artist intended. DTS-HD Master Audio delivers surround audio that is indistinguishable from the original soundtrack or music recording. The new high definition optical discs have far more capacity than standard DVDs, which has allowed DTS to develop a surround sound format to deliver surround sound at super high bit rates - up to 24.5 Mbps on Blu-ray discs and 18.0 Mbps on HD-DVDs that are vastly superior to standard DVDs. This bit stream is so “fast” or the transfer rate is so “high” that it can deliver Lossless Audio, a “bit-for-bit” recreation of the original recording. The result is 7.1 channels of audio that are identical to the original studio master. With DTS-HD Master Audio you will experience movies and music exactly as the artist intended.

Conclusion
“Close Encounters of the Third Kind – 30th Anniversary Ultimate Edition” is one of the first Blu-ray Discs that include both Dolby True HD and DTS HD Master Audio soundtracks. The aural experience derived on this special disc set is nothing short of amazing giving you the feeling that you really are atop the Devil’s Tower with the government officials. The floor literally shakes as the Mothership touches down. This is what home theater is all about!

Which is better? Like beauty, it’s in the eye (or ear) of the beholder. Personally, I prefer DTS, and chose it on any disc that I watch or listen to. I believe that I hear more subtly and nuance in the sound presentation. However, others may prefer Dolby Digital decoding, which sounds pretty awesome also. If you’re watching “Lost” on your local ABC-HD channel, for example, the Dolby Digital soundtrack certainly adds depth and presence to the experience. Don’t you just love home theater!!! Pass me the raisonettes.

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Dennis P. Barker - Contributing Writer
Dennis has been involved with Consumer Electronics forever it seems. His 25+-year career includes a 12-year tour of duty at Consumer Reports magazine, as well as stints as a product reviewer, market analyst, technical editor, and consultant for the electronics industry. He lives in Ossining, NY with his two children, one demanding cat and piles of A/V equipment.

Surround Sound Chart

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