Is DTS MDA the Future of Audio?

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DTS Multi-Dimensional Audio Demoed ... For Real

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Several companies are pushing the idea of surround-sound systems with more than 7.1 channels of sound, otherwise known as immersive audio. You may have heard a lot about -- and probably actually heard -- Dolby Atmos, which has been used in close to 100 movies and is currently installed in more than 300 theaters worldwide. There's also the Barco Auro-3D system, which, as of 2014, is in about 150 theaters and has been used on more than 30 movies. Behind the scenes in the movie production community, though, a consortium of pro audio companies, coordinated largely by Dolby competitor DTS, has been pushing a different idea: Multi-Dimensional Audio, or MDA.

DTS conducted demos in a specially outfitted theater in the Los Angeles area.

Fortunately, I happen to live within an hour's drive of that theater and I was able to get an extensive MDA demo, early in the morning before the theater opened. I usually leave the surround-sound coverage to About.com Home Theater Expert Robert Silva, but because immersive sound will almost certainly affect stereo systems someday, I thought I'd take the chance to hear what MDA can do.

Follow along with me and I'll explain how MDA works ... and what it sounded like.

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MDA: How It Works

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About.com Home Theater Expert Robert Silva has already explained MDA in depth, but here's the basics. With a 7.1-channel system in a home theater or commercial cinema, you have front left, center and right speakers; two side surround speakers; two rear surround speakers; and one or more subwoofers. Some audio/video receivers can kick this up to 9.1 or 11.1 by adding front height speakers and/or an extra pair of speakers between the front left/right and side surround speakers, using either Dolby Pro Logic IIz, Audyssey DSX or DTS Neo:X processing to derive the extra channels.

Immersive systems take this a step further by adding speakers on the ceiling to provide more enveloping and realistic surround effects. They can also add more speakers to the front left, center and right speakers already behind the screen, and extra surround speakers in arrays positioned above the existing arrays. These speakers may be set up so they can be addressed individually, so that a sound effect can be isolated to one specific speaker. Or a panning effect can travel smoothly and consistently around the theater, moving among, say, 16 or 20 separate surround speakers instead of among four groups of speakers as in 7.1.

Dolby Atmos is, in essence, a bunch of extra channels grafted onto a conventional 7.1 system. The speakers can be addressed in groups as in 7.1, or individually for more immersive effects, and there are also two rows of ceiling speakers added.

MDA can address all the same speakers, and more -- the demo I heard uses three rows of speakers on the ceiling plus two additional height-speaker arrays of side surround speakers located above the conventionally placed side surrounds, plus additional left, center and right height speakers on the top of the screen.

John Kellogg, DTS senior director of corporate strategy and development pointed out, “We're not suggesting you need all these speakers for immersive cinema. This installation was really put together as a lab so we can test and demonstrate many combinations of speakers. This installation includes speaker configurations that currently exist in cinemas and ones coming in the future. But of course using them all is really fun.”

The key technical difference with MDA is more a way of thinking about the mix and the audio soundfield.

MDA is what's called an "object-based" audio system. Each bit of dialogue, each sound effect, each snippet of soundtrack music and even each instrument in a soundtrack mix, is considered to be an audio “object”. Rather than recording sounds onto a specific channel or group of channels -- a two-channel stereo recording, or a 5.1- or 7.1-channel multichannel soundtrack, for example -- they are all exported as part of an MDA file. The file includes metadata that assigns a certain coordinate or physical position to each sound or audio object; plus the time at which the sound appears and the volume at which it plays.

"The speakers become more like pixels than like channels," Kellogg said.

MDA can "map" these vectors to any array of speakers, from dozens of speakers in a commercial cinema to as few as two in, say, a TV set. (Of course, all of Dolby's surround technologies, including Atmos, include the capability to be reduced to as few as two channels.) When an MDA system is installed, a technician feeds information about the speaker locations in that particular room into the system, and the rendering software figures out how to use the array to best reproduce each sound. For example, if a surround effect is supposed to come from, say, 40 degrees above you and 80 degrees to the right, there might not be a speaker at precisely that point, but MDA can create the phantom image of a speaker at that point by piping the correct mix of sound into the speakers nearest that point.

From a business standpoint, MDA is also very different from Atmos. The Atmos system and program is proprietary and governed by Dolby. MDA, in contrast, is an open format, reflecting a collaboration among cinema industry companies including DTS, QSC, Doremi, USL (Ultra-Stereo Laboratories), Auro Technologies and Barco, and a few studios and exhibitors.

(At this point I should add a disclaimer. I worked for Dolby from 2000 to 2002, but I have had no financial connection to the company since. I wrote a white paper for DTS last year about an unrelated technology. Currently I am not pursuing and have no intention of pursuing work with either company. I don't have the in-depth knowledge of the movie production and exhibition industries that would be required to make an informed prediction about the future of either of these systems, and frankly I don't care. I'm just writing about a cool demo I saw.)

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MDA: The Gear

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QSC cinema sales engineer Paul Brink was on hand to take me through the whole signal chain up in the projection booth of the specially equipped theater. The core of the system is a QSC Q-Sys Core 500i digital signal processor, which has the capability to handle as many as 128 inputs and 128 outputs. The Core 500i takes digital audio and metadata from the Doremi server used to play the movie off the hard drives supplied by the movie studios. The Core 500i connected to 27 QSC DCA-1622 amplifiers through five Q-Sys I/O Frames, which are essentially networked digital-to-analog converters. You can see all of these components in close-up on the next page.

This system powers 48 channels of sound plus a subwoofer channel feeding seven subwoofers. As I explained previously, the array in the theater included:

1) Left, center and right speakers behind the screen
2) Left, center and right height speakers above the screen
3) Three rows of ceiling speakers running front to back
4) Surround speakers running all around the side and back walls
5) A second higher array of surround speakers on each side wall, positioned about 6 feet above the main array.

Obviously, the cost of such an array can be high, and installation -- especially of the ceiling speakers -- expensive. "Scaffolds had to be erected and taken down 15 separate times to mount the ceiling speakers up there," Kellogg said. "But it doesn't have to be that complicated. It can be whatever the theater can afford. In a theater where it's not practical to put in full ceiling arrays, we usually recommend two near the front, two near the back, and one in the center of the ceiling. We find that's critical for giving you that 'voice of God' effect."

One of the coolest things about the demo was that Brink controlled it all from his laptop computer while sitting in the theater with me, and could reconfigure the system in seconds. This capability allowed him to give me the full MDA effect with all speakers, and then to reconfigure the sound into different speaker arrangements in locations similar to those typically used for Atmos and Auro-3D, as well as for standard 7.1.

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MDA: The Experience

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The material for the demo was the 10-minute sci-fi short Telescope, which you can see on the movies's own site or watch on YouTube (but just in 2.0, not 48.1). For the demo, a special MDA mix had been created, with the sound effects existing as vectored objects and the QSC Core 500i deciding which speaker or speakers to route the sound objects into. Through his laptop, Brink was able to map the objects to the different array configurations I discussed before.

The mix sounded good on all of the various arrays, even the 7.1, and the fundamental character of the sound didn't change. What changed was the sense of envelopment. Just as direct comparisons with 5.1 and 7.1 reveal the limitations of stereo, direct comparisons of MDA with the other configurations revealed their limitations.

Telescope takes place entirely in the cabin of a tiny spaceship, and this, surprisingly, showed off MDA to full effect. When the ship isn't warping off through space, the sound effects are mostly little bleeps and bloops and hums from all the machinery around the cabin. With MDA, I simply got a more complete and seamless sense of envelopment than I got with the other immersive formats, and a far more realistic effect than I heard from 7.1.

Each time the ship warped to a new location, the front-to-back swooshing effects were substantially smoother with MDA and Atmos, and because of the extra ceiling array I heard more differentiation in these effects.

Based on this demo, at least, MDA sounds to me like the most advanced thing going in sound. But of course, I'm sure the sound effects were mixed to show off MDA. It's up to the mixing engineers to make use of this extra capability. For MDA to have a sonic advantage in real-world applications, the mixing engineers will have to have the time, budget and desire to create mixes that exploit its capabilities.

What's this mean for home audio systems? As of 2014, there's no plan for that yet, at least not one DTS is willing to discuss. But with rumors flying about a launch of Atmos-capable A/V receivers, it's hard to imagine DTS doesn't have the home market in mind.

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