DTS

The following week found us at DTS’ facilities in Agoura Hills, just northwest of Los Angeles. There we had a tour of their deluxe screening room, and soon found ourselves in one of their demonstration sound studios, where a 7.1 system featuring seven KRK Expose E8T monitor speakers was teamed with two Bag End PS18E subwoofers. In lieu of a stack of power amplifiers, this system was instead easily powered by a Denon AVR-2808CI audio/video receiver, and we were treated to a number of high resolution audio and HD video clips from the latest DTS Blu-ray demonstration disc.

After an informative presentation which explained the benefits of their latest codec technologies, we dove right into the A/B comparisons between the original PCM versions and the various DTS codec’d versions. The short clip chosen for us came from a DTS Blue Man Group recording, again using a spare, sparse selection for an easier and more revealing A/B comparison. Again, we found no differencebetween the uncompressed original track and the DTS-HD Master Audio version.

In addition to the DTS HD-Master Audio lossless codec, DTS also offers up a nearly lossless high bitrate format called DTS-HD High Resolution Audio, with up to four times the bitrate of their core DTS format, which we were able to audition via their Blu-ray demonstration disc. We then conducted A/B comparisons between the high resolution Blue Man Group PCM original soundtrack and the core DTS codec which has a Blu-ray and DVD bitrate of either 768 kbps or 1.5 Mb/s, in a somewhat similar but not totally blind fashion that we went through the week before.

It was déjà vu all over again. We switched back and forth between the original PCM master and the core DTS version, and here we found only the slightest, barely noticeable difference. From a frequency response standpoint, both versions were identical, with clearly delineated high frequency details, but the compressed version differed slightly only in barely noticeable presence —that sense of being “there”, with the original PCM track having just slightly greater overall richness. Whatever acoustic elements were removed in the code/decode process were clearly superfluous, at least for the most part, as the audible differences were so minor as to be almost unnoticeable—again, another testament to the capabilities of this highly refined codec.

A/V receiver and surround processor makers are quickly adding these advanced decoders in their new model offerings, and broadening the price range to a wider audience, with A/V receiver models so equipped priced at under $600 available later this summer. Owners of Sony’s Playstation 3 gaming console got the DTS-HD Master Audio decoder as a freebie this past spring, as a feature added during a PS3 system software upgrade, and more HDMI version 1.3 Blu-ray players that can pass these high resolution bitstreams to downstream high resolution surround decoders are entering the market as well.

Conclusion
From both listening sessions, I came away with a newfound respect for the abilities of these audio codecs to deliver excellent sound quality at dramatically reduced bitrates. Ideally, I’d like to see future Blu-ray releases moving away from bit-hog multi-channel PCM tracks and instead use one of these high resolution codecs, as a typical Blu-ray movie’s 5.1 channel PCM soundtrack consumes a whopping 6.9 Mb/s all the time. That’s a large chunk of a disc’s available bitspace, some of which could be better used for maximized video coding precision, for example.

These new high-resolution codecs are backwards compatible with existing decoders, but only in their most basic form. For the better sound you'll need either a player that decodes (and sends that audio out via PCM over HDMI or analog 6-channel out) or a receiver/processor that decodes the format, and a player that will output the bitstream of these codecs.

Dolby Digital Plus and DTS-HD High Resolution offer tremendous sound quality and are extremely efficient for the quality they provide. While still compressed audio, they're closer to the original master than most people will be able to hear.

For those who will settle for nothing but the best, the bit-for-bit accuracy of Dolby TrueHD and DTS HD-Master Audio provide them the confidence that what they’re listening to at home is identical as the original studio master soundtrack.

So Subtle
What impressed, or perhaps surprised, me most about these tests was how good the base codecs actually are. The difference between the original audio and the basic Dolby Digital and DTS is a lot subtler than you’d expect, given the extreme amount of compression (around 10:1, a similar ratio to that of 128 kbps MP3).

That said, I could definitely pick out the difference between the lesser (or perhaps it’s more accurate to say “better”) compressed versions and the higher compressed versions. The difference is mostly in the presence, or ambience. The lossless, Dolby Digital Plus, and DTS-HD High Resolution compressed tracks were just a little more open and airy. I hate to say it, but they just sounded more realistic and transparent. The 448 kbps Dolby Digital and standard DTS tracks were less so, a little more closed off. Between the 640 kbps Dolby Digital and the uncompressed, the difference was even less noticeable. Enough so that most people, even those trained to listen for it, probably won’t be able to hear the difference.

The core DTS call is a little harder, as there wasn’t the same blind system in place to A/B as precisely as at Dolby. Results were similar, though.So by all means go for the new codecs, as they definitely sound better than what was on DVD. Uncompressed PCM, on the other hand, is just a waste of space (though compatible with everything).

If you’ve been listening at home and are sure you can hear a difference on your favorite discs, be wary. There is absolutely no way to tell that compressed and uncompressed tracks on any disc have anything to do with each other. They could come from different masters, they could be mixed differently, or any number of other variables that makes an in-home test, unfortunately, impossible. That said, trust your ears, and go with the one that sounds best to you. –Geoffrey Morrison