Holographic Imaging Through Science?</h1>
Several weeks ago I began a blog series to discuss Audyssey’s new DSX surround sound system, and this entry will be the wrap-up to the series. Let’s begin with a brief review.
Recap: What is Audyssey DSX?
Audyssey DSX is a new surround system designed to leverage and build upon the strengths of conventional 5.1 or 7.1-channel surround systems by adding two new types of channels: namely, width channels and height channels. (To accompany this blog, Audyssey has graciously provided a set of five system configuration diagrams that show several variations on the DSX theme.). The DSX system is designed specifically to augment music or movie material originally recorded in a 5.1-channel format.
Working from research data gathered in the USC Immersive Audio Lab, as well as from research data gathered by perception psychologists, Audyssey designers found—not too surprisingly—that listeners benefitted most from spatial imaging cues that helped define the front (as opposed to the rear) half of the soundstage. Specifically, they found that in most 5.1-channel systems there are typically what might be termed sonic “information gaps” to the front left and right of the soundstage. The Audyssey DSX system’s width channel speakers, which should ideally be placed 60 degrees to the left and right of the system centerline and positioned at ear level, are meant to fill in those gaps to the sides of the soundstage.
Audyssey co-founder and USC Professor of Film Sound Tomlinson Holman explained that there is a definite “pecking order” within the hierarchy of benefits offered by Audyssey DSX, and that the greatest single benefit comes through using the system’s width channels. Interestingly, Holman commented that, given a choice between setting up a conventional 7.1-channel system (that is, one with pairs of side-surround and rear-surround speakers placed behind the listener) versus a DSX-type 7.1-channel system (that is, a conventional 5.1-channel system augmented with two width speakers positioned in front of the listeners), the DSX system would give far more convincing and immersive results.
However, another striking benefit of the DSX systems involves the possibility of adding height channel speakers, which should be placed at 45 degrees to the left and right of the system centerline and elevated to a 45 degree up-angle relative to the listener. In practice, the height channels serve two purposes. First, height channels help add a vertical component to the surround soundstage image, conveying—where possible—information that would be heard if a sound source moved upward or even passed up and overhead within the stage. In a demo conducted by the Audyssey team, a favorite example, and one that wowed the assembled A/V journalists, was a scene from the film Wall-E, where audience members could not only see but also the Wall-E robot character (who moves about within his world on a small pair of caterpillar treads) climbing up an ramp-like incline on the side an enormous mountain of trash.
But another aspect of the height channels involves their ability to mimic a type of spatial cue that we all experience whenever we hear sounds that originate within enclosed spaces; namely, ceiling reflections. To a greater extent than one might at first think, Holman said, ceiling reflections help us gauge and recognize the size and acoustic qualities of various listening spaces (the interior of an aircraft hangar, for example, sounds markedly different than the interior of Carnegie Hall). The Audyssey DSX height channels help us make better, more coherent sense of the reverberant cues that we hear in scenes (or musical events) recording indoors. Or at least that’s the theory.
How Does DSX Sound In Practice?
DSX sounds quite good, effectively turning the “circle of sound” (or perhaps I should say “partial circle of sound”) heard in some surround systems into a more fully enveloping of sound, as if you, the listener, are seated smack-dab in the sweet spot beneath the center of an overarching dome of sound. That said, however, I am also compelled to observe that the extent to which you find DSX impressive may vary in direct proportion to the quality of the systems you’re used to hearing.
To be perfectly honest, I found the Audyssey DSX demo system sounded better than some surround (and high-end stereo) systems I’ve heard in terms of holistic, holographic imaging, but not by nearly as large a margin as some of my fellow editors seemed to experience. I suspect this may have to do with two factors.
First, I’m used to hearing some very high-end stereo systems that offer strikingly good resolution, focus, and pinpoint imaging, and that produce extremely wide and deep soundstages. What those stereo systems may give up relative to DSX in terms of producing an all-encompassing “dome of sound” is offset by their almost eerie clarity, imaging precision, and giant soundstages (albeit with no true surround information coming from behind listening position).
Second, I’m very particular about the imaging of my surround sound systems and am used to tweaking them painstakingly until I not only hear a good, coherent front soundstage, but one that also wraps smoothly to the sides of the room. Granted, I sometimes achieve these results by deliberately positioning my front main speakers somewhat more widely angled toward the sides of the listening space than is theoretically correct. (In theory, the front mains should be positioned roughly 30 degrees to the left and right of the centerline of the system, though I’ve been known to position my main speakers at wider angles than that.). But here’s my thought: I’d rather go with a set-up that is a bit wrong in theory yet that sounds right, as opposed to putting up with the opposite situation (i.e., a system that is theoretically correct, but sounds wrong—yuck!).
At the end of the day, I suspect that the Audyssey DSX system may provide a more reliable and foolproof means of achieving the kind of immersive and holographic surround sound environment we all crave.
At the same time, I think you can get many—though perhaps not all—of the core benefits of DSX technology by carefully setting up either 5.1-channel or even 2-channel systems, using high quality components and paying very close attention to speaker placement (not to mention judicious use of acoustic treatments).
DSX Caveats and Questions
It perhaps goes without saying that one of the inevitable caveats of setting up a DSX system is complexity. In full-blown configurations, DSX systems require nine (or even 11) speakers, not including subs, which—I suspect—is more than many home owners will want to accommodate (except in full-on, dedicated home theater rooms). Even then, properly positioned height channel speakers may pose a problem in that they may need to be mounted near the ceilings—if not in the ceilings of some rooms. It may be, though, that some accessory-makers will devise tall, attractive stands (perhaps with height-adjustable poles?) for use with height channel speakers, assuming the DSX concept catches on.
An open question is whether or not the DSX system is "sweet spot-centric." I don't know the answer to this question, but it arose in a private talk I had with Tomlinson Holman after hearing the DSX demo in the Audyssey listening room. I had the sense that I had experienced most but perhaps not quite all of the benefits of DSX and I asked Holman about the matter. He asked me, "Were you sitting in one of the center seats?" I replied that I had been seated one chair off from the center position. "Then you should try it from the center," he said. Unfortunately, a glitch in the room's media server prevented us from re-trying the demo, but Holman's comment left me with an open-ended question.
Normally, Audyssey’s MultEQ room/speaker EQ system (which I greatly admire) is all about broadening the sweet spot, so that almost every seat in the room becomes a viable listening position. Wouldn’t it be odd if the DSX system, in sharp contrast to Audyssey’s MultEQ system, made systems more finicky in terms of requiring listeners to sit in the “sweet spot?” Only time (and further listening sessions) will provide answers to this one.