Playback Learns About Audyssey DSX: Part 3
Holographic Imaging Through Science?
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 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.
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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.
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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.
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 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.
Discussion Topics
- Review of Hyperion 968
- Magico Ultimate II Horn Loudspeaker- Following A Dream- Tom Martin
- What is it about B&W speakers (and Rotel electronics) that they are sold in so many stores ?
Speakers
- Repurposing The Beatles; "Love" & Cirque du So
- The Beatles Remasters on Vinyl
Music - Rock/Pop Reissues
- Integrated Amplifiers...which one & how to choose
- Need Recommendations for new Audio/HT setup
Comments
The original Chesky SACD demo disk has a section of 6.0 music (no center and no LFE), with the extra 2 speakers located in roughly the position recommended by Tomlinson. These tracks clearly produce a more realistic front image. Several of the early Telarc and DMP SACD's are 6.0, with the LFE channel assigned to a mono height channel. Here, the sense of envelopment is stronger than usual, even though the muscians do not move (as WALL-e does). My experience with the Chesky and Telarc recordings suggests DSX is a good idea.
The original Chesky SACD demo disk has a section of 6.0 music (no center and no LFE), with the extra 2 speakers located in roughly the position recommended by Tomlinson. These tracks clearly produce a more realistic front image. Several of the early Telarc and DMP SACD's are 6.0, with the LFE channel assigned to a mono height channel. Here, the sense of envelopment is stronger than usual, even though the muscians do not move (as WALL-e does). My experience with the Chesky and Telarc recordings suggests DSX is a good idea.
As we add more speakers to the system, we add complications. Just from the acoustical side, we add at least 6 more first order reflections with each additional speaker, along with many other boundry effects which will increase spatial and timbre distortions. Though I enjoy multi-channel audio, a two channel system, when set up properly, can offer a very large, holographic soundstage and is much easier to tame.
Sure, add more speakers around and sound comes out of them, but how accurate and reproducable is it? A good soundstage requires symmetry of acoustics and electronics. As we add more channels, symmetry becomes less and less likely. Removeing room acoustics from the equation, a good soundstage is obtained by signals converging at a single point in space, at the same time with the same gain. System calibration is critical. In addition, the system components need to be the same for each channel in order to have the possibility of reproduceing the same. Adding more channels makes this possiblity much more difficult to achieve. I wish for a 4.2 system. With such a system, more people would be able to afford, accomodate, and faithfully reproduce a convicing soundstage.
Norman Varney
A/V RoomService, Ltd.
I agree that adding more channels does add spatial and timbre distortions. Fortunately I have a dedicated listening room where I can experiment with multiple channels and diffusion (mostly, LP's and books) and absorption. With a little effort (and not much absorption) nearly all spatial distortions can be tamed, a least at the "sweet spot". I let Audyssey handle timbral problems, which it does very well. The part of your comment that caught my eye was your interest in 4.2 systems. My experience is that it is very difficult--so far for me, impossible--to get truly deep bass (say, below 30 Hz) with more than one subwoofer. Have you set up a system the plays below 30Hz with more than on subwoofer? If so, how did you do it?
I'm not sure I understand your question. If you can produce frequencies below 30Hz. with one subwoofer, you can certainly do it with two. The reason I say .2 is becuase I don't desire a monoral signal from 80Hz. on down. 80Hz. reproduced in a small room is not omni-directional, you can easily perceive where the signal originates, and therefore a single subwoofer draws attention to itself. It does not integrate with the system as a single voice, rather it sounds like the low frequencies are coming from its location. The illusion is segregated.
Norman Varney
A/V RoomService, Ltd.
"My experience is that it is very difficult-so far for me, impossible-to get truly deep bass ..."
Provided your audio system has what it takes, your problem probably has more to do with the room than with the audio system.
Since I have three subwoofers (a JL 13" and the two bass units from an Infinity full range that can be separated) and a processor that allows for up to three subwoofers, I've tried one, two and three subwoofers in what I guess is a moderately sized room (19x21x9, roughly). I've used the RPG software to find the best locations and have also tried putting the second subwoofer at the listening position and crawling around to find locations where the signal is reinforced. Invariably, adding a second or a third subwoofer (always equalized to remove room peaks) adds to bass frequencies from about 45 Hz to 100 Hz (that is, lots more bass drum) but subtracts from the signal in the really deep bass. While I agree that, at least on some recordings, deep bass from a single sub can be located, with time it's possible on most recordings to adjust the level so that the deepest bass appears to come from the recorded space even when the sub is located well away from the font speakers.
Obtaining somewhat linear bass frequency response shouldn't be too difficult with your equipment. I'm thinking that you might be locating your sub(s) in areas that are problematic pressure peaks. If you locate them in pressure troughs for those frequencies, they will not boost them. Idealy, the sub(s) should be physically time aligned with the mains and placed between them, off the floor, so as to avoid boosting your fundamental axial room modes. After this is done, calibration can be performed.
Norman Varney
A/V RoomService, Ltd.
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