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RE: Sound coming from outside of the soundstage

Posted by josh358 (P) on March 17, 2012 at 15:51:10

In Reply to: RE: Sound coming from outside of the soundstage posted by Satie on March 17, 2012 at 14:04:17:

I was taken in by that article of Robert Harley's but there was a discussion of it and somebody read the patent. Seems all he's doing is (primitive) crosstalk cancellation. You can do it better with the free Ambiophonics software, even better than that with Princeton's no-longer-free BAACH filter.

The role of time alignment/group delay in imaging is something I don't understand -- that is, I don't know whether it improves it or not, as long as the group delay is the same for both channels, since the brain does use interaural time differences (relative phase at lower frequencies, useless higher up where the wavelength is small compared to head width making the directional information ambiguous). Some recordings preserve this (e.g., dummy head or ORTF head-spaced cardioids), some don't (e.g., spaced omnis, in which the relative phase is randomized or pan-potted multiple mono).

I've seen it said that polar phase response is important to imaging. This would be because as you say the brain has to match the reflection up with the direct sound to determine that it's ambiance and extract information from it. If the polar amplitude response goes off, the polar phase response will as well, so who knows where one leaves off and the other begins. However, logic suggests that the brain determines this by using the neural network equivalent of a tapped delay line, and subtracting signals at t, t-1, t-2, etc. to some limit, then seeing if they null. And I'd guess that what it does by way of being able to do this simultaneously in multiple frequency bands, over different apertures, etc. is constrained by evolution, that is, by natural phenomena in which the group delay of a reflected image is generally the same as that of the source. In any case, as I said in an earlier post, I don't think different crossover alignments tell us all that much precisely because they do radically change the polar amplitude response, so we're left with that ambiguity. And we do know that polar amplitude response is critically important to matching the reflections with the source, there's much on Linkwitz's site about that. Maybe someone has done some experiments to resolve it, but if so I haven't seen them mentioned.

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