A few months ago we talked about Dolby and DTS surround formats. There certainly are a lot of them. Soon there will be more—andthat’s our subject for today. Why, why, why? I can just about hear you all asking. Are the next-generation surroundformats just another blind lunge for licensing revenue? Or do these companies simply delight in torturing us? Believe it or not,there is a legitimate reason to move surround into a new generation. Actually, two reasons. One is that the bit bucket represented by DVD has gotten larger with the advent of the HD DVD and Blu-raydisc formats. The other is that the bit bucket has shrunk to a thimble in other areas—think satellite and streaming. To fill the newly enlarged bit bucket, Dolby and DTS are going lossless. Andto fill the thimble as shrewdly as possible, Dolby in particular has brought its lossy technology to new heights of sophistication. Let’s get some background out of the way. What’s the difference between lossless and lossy encoding formats? Lossless ones pare down digital data while still regenerating the originalstudio-master sound source bit for bit, omitting nothing—you hear what the mixing engineer heard. For audiophiles, this is a proposition we can’t refuse. Lossy formats use perceptualcoding to omit some (often quite a lot) of data to fit the signal into narrow channels. Examples include not only Dolby Digital and DTS but also MP3, WMA, and the AAC format used by iTunes (did youknow Dolby developed that one?). More background: Dolby’s existing formats include Dolby Digital, the main surround formatused in DVD; Dolby Digital EX, which expands Dolby Digital 5.1 to 6.1 or 7.1 speakers; and Dolby Pro Logic II and IIx, which decode ancient analog surround as well as adapting stereo sources tosurround. On the DTS side, there is DTS 5.1, often used on DVDs as a higher-quality alternative to Dolby Digital; DTS-ES, the 6.1-channel version of DTS; DTS 96/24, a lossy high-resolution formatused on some DVD-Audio releases; and DTS Neo:6, which deals with analog surround and stereo signals. Now the fun begins! By the timethis is done, you’re going to hate me. The Next Generation in Surround Dolby TrueHD will bring surround sound to new heights of quality. It’s alossless—as opposed to uncompressed—format. That means it reduces the original signal to something that takes up less space on a disc while omitting not a shred of sound quality. Theformat supports up to 14 full-range channels, which means we may someday see height channels and other configurations beyond the current 7.1 channels. Dolby TrueHD’s data rate can go up to awhopping 18 megabits per second, more than 40 times the maximum rate of Dolby Digital. If Dolby TrueHD shows Dolby working harder toproduce better surround, Dolby Digital Plus shows Dolby working smarter. It also supports 14 channels, at data rates from an ultra-skinny 96 kilobits per second to a more generous 6 megabitsper second. That’s quite a range. Dolby Digital Plus can approximate the quality of existing Dolby Digital at half of the latter’s data rate, which in practice is 384-448kbps. But give itmore bits and it can enlarge the soundfield, make highs feel less edgy, and make vocals more intelligible (with what Dolby calls dialogue normalization). Dolby Digital Plus is already being used inEuropean satellite video delivery. You can also expect to see it operating at the lower end of its scale with streaming applications. The DTS version of lossless surround is called DTS-HD Master Audio. It runs at a variable data rate of up to 24.5Mbps or a constantdata rate starting at 1.5Mbps. I’m told the variable data rate kicks in when a soundtrack peak—like an explosion, or the roar of a crowd—exceeds the limits imposed by the bit bucketitself. By way of comparison, the existing DTS 5.1 and DTS-ES formats run from 768kbps-1.5Mbps, so Master encodes significantly more data. Master encodes 7.1 discrete channels (with room forexpansion, I suspect) at resolution of up to 24 bits and 192kHz, compared to 16 bits and 44.1kHz for the CD. DTS is also unveiling anew lossy format that falls somewhere, in quality, between DTS-HD Master Audio and old-style DTS 5.1 and DTS-ES. This is DTS-HD High Resolution Audio. It runs between 1.5 to 6Mbps. In software, you may see some titles labeled DTS Encore. This is simply a relabeling of the old DTS 5.1, DTS-ES, and DTS 96/24formats. They use what DTS calls core data; the new formats add extension data to encode more information. Limits of HD DVD and Blu-ray So far we’vedescribed the inner and outer limits of these surround formats. What we haven’t discussed is how they’ll be implemented in the new disc formats—and what interfaces you’ll needto get them into your system. First of all, while all these formats are supported in HD DVD and Blu-ray, there are degreesof support. Some are mandated, but most are optional. That means you may or may not see them in hardware and software. And most of them don’t run at their maximum data rates in the new discformats. On the hardware side: Dolby TrueHD runs at its full data rate of 18Mbps in both HD DVD and Blu-ray. Dolby TrueHD ismandatory in HD DVD and optional in Blu-ray. Dolby Digital Plus, capable of a maximum of 6Mbps, runs at 3Mbps in HD DVD and 1.7Mbps in Blu-ray. Again, it’s mandatory in HD DVD, and optional inBlu-ray. It’s noteworthy is that HD DVD is allowing higher data rates than Blu-ray for Dolby Digital Plus even though HD DVD’s disc capacity is slightly smaller than Blu-ray’s. Remember when we said DTS-HD Master Audio runs at up to a variable data rate of 24.5Mbps? In Blu-ray, it actually runs thathigh—hooray!—at least for soundtrack peaks. In HD DVD it runs at a still pretty impressive 18Mbps. DTS-HD High Resolution Audio, capable of a maximum of 6Mbps, runs exactly that highin Blu-ray, and at 1.5-3Mbps in HD DVD. Both of these formats are optional in both HD DVD and Blu-ray. What’s noteworthy here is that Blu-ray is allowing higher data rates for these new DTSformats than HD DVD, a reversal of the situation with the new Dolbys. Limits of Interfaces There are three ways to get these new surround signals from your newHD DVD or Blu-ray player into your receiver. In order of preference they are: the HDMI interface, the analog interface, and the optical or coaxial digital interfaces. You read that right—analogmay be better than the older digital interfaces. The catch is that analog will work well only if your receiver has bass management for the 5.1-channel analog line inputs. HDMI comes in different versions from 1.0 to 1.3. If you want Dolby TrueHD, Dolby Digital Plus, or DTS-HD High Resolution Audio,you’ll need HDMI 1.1 or 1.2, which some newer receivers have. Your receiver won’t be able to decode these formats, but that’s OK, because all the necessary decoders, panners, andmixers are built into the players. But if you want to route DTS-HD Master Audio to the receiver via HDMI, you’ll have to wait for HDMI 1.3. That newest version is not yet available in receiversbecause the manufacturers are waiting for the latest HDMI chipsets to become available. When HDMI 1.3 becomes a reality, receivers may acquire built-in decoding for the new formats—someaudiophiles may prefer to move the bits into the receiver and decode them there. But that’s in the future. If you’drather live in a simpler world, the good news is that any of the Dolby or DTS formats, new or old, can run from the player into your receiver via the analog line connections, either 7.1 or 5.1,whichever one your receiver has. Again, that’s because the decoders are built into the players. But there’s a catch. If your receiver doesn’t have bass management for theanalog-ins, you’ll have to depend on the bass management in the player, which may or may not be very good, if it’s there at all. This isn’t a problem if you’re runningfull-range speakers all around, but if you’re like most of us, you have a sub, and the crossover between speakers and sub is crucial to the performance of your system. In that case, you havetwo options. Either upgrade to HDMI (or wait for 1.3, if possible) or use your receiver’s existing optical or coaxial digital jacks so you can use your receiver’s bass management. The only thing wrong with the optical and coaxial jacks is that their constrained bandwidth does not allow the full resolution ofwhich these new surround formats are capable. With Dolby TrueHD and Dolby Digital Plus, the signals will get downconverted to 640kbps. That’s more than the usual 384-448kbps of Dolby Digital asit’s implemented on the majority of existing DVD releases, so you may still hear an improvement in sound quality. With DTS-HD Master Audio and DTS-HD High Resolution Audio, the downconversionis to 768kbps, same as original DTS 5.1 and DTS-ES. If you’re an early adopter, here’s something else you need to know:First-generation players don’t fully support these new formats. I’d need another 1000 words (and another week of research) for a definitive survey, but let’s take Dolby TrueHD as anexample. Toshiba’s first two HD DVD models support TrueHD only in stereo! However, a firmware upgrade has raised it to 5.1 channels. Panasonic’s first Blu-ray player will supportDolby Digital Plus but not TrueHD. However, again, a firmware upgrade will fix that. Of course, you need software as well ashardware to make these new formats work. Warner is the first studio to announce Dolby TrueHD titles. As for Dolby Digital Plus, my source at Dolby tells me that Universal is encoding it at acomparatively generous 1.5Mbps, Paramount at 768kbps, and Warner at 640kbps. Sony is encoding old-style Dolby Digital at a new-style 640kbps. Incredibly, some HD DVD and Blu-ray releases are usinguncompressed PCM (pulse code modulation, like a CD except fatter) in lieu of the new lossless surround formats. This may save them a few pennies on licensing but wastes a lot of space on the discthat could be used for higher video quality or extras. Your best sources for further information are the enthusiast sites—I can’t even begin to keep track of the latest software news, tryas I might. Limits of Patience The only reason I can rattle off all this stuff is becauseI’ve been researching it for the next edition of my annually updated home theater book—87,000 words of joy! Trying to understand these new technologies was hard, and as you’veprobably figured out by now, explaining them in a clear, simple, useful manner is virtually impossible. Though I intend to get a lot more practice. If you have any further questions, please asksomeone else! Mark Fleischmann is the author of Practical Home Theater. audio editor of Home Theater Magazine, and tastemaster of happypig100.com. Edit 9/22/06 – replaced: On thehardware side: Remember when we said Dolby TrueHD can run at data rates to 18Mbps? Well, in HD DVD, it can run only up to 6Mbps, though that’s still a vast improvement. In Blu-ray, the data rate iscut in half again, to 3Mbps. Dolby TrueHD is mandatory in HD DVD and optional in Blu-ray. Dolby Digital Plus, capable of a maximum of 6Mbps, runs at 3Mbps in HD DVD and 1.7Mbps in Blu-ray. Again,it’s mandatory in HD DVD, and optional in Blu-ray. It’s noteworthy is that HD DVD is allowing higher data rates than Blu-ray for both of these new Dolby formats even though HD DVD’s disc capacity isslightly smaller than Blu-ray’s. …with this:
On the hardware side: Dolby TrueHD runs at its full data rate of 18Mbps in both HD DVD and Blu-ray. Dolby TrueHD is mandatory in HD DVD and optional in Blu-ray. Dolby Digital Plus, capable of amaximum of 6Mbps, runs at 3Mbps in HD DVD and 1.7Mbps in Blu-ray. Again, it’s mandatory in HD DVD, and optional in Blu-ray. It’s noteworthy is that HD DVD is allowing higher data rates than Blu-rayfor Dolby Digital Plus even though HD DVD’s disc capacity is slightly smaller than Blu-ray’s.
