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.
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 sides 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 hear 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.
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 hemisphere 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.