On 05/24/2011 07:42 PM, Lee ponzu wrote: > I saw this cool demo of 3D sound. This is totally different from the > SL Voice technology, and I think it would compliment it perfectly. > > Take a look... > > http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=princeton+3D+sound > <http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=princeton+3D+sound> OK, let's see. (Haven't watched the video <http://www.princeton.edu/3D3A/> fully, yet, as I can't turn up the speakers where I am right now.)
> The basic idea is that stereo gives a weak illusion of 3D. Oh? Stereo can give you the most perfect illusion of 3D, /when listened to over headphones/ and mixed or recorded for headphones. Listen to the popular "virtual barbershop" recording to know what I mean. The only real problem there is that when you turn your head, the sound sources seem to turn with it, while the picture on a screen won't move. (Off course, with VR glasses instead of a fixed screen, you don't have that problem.) The challenge is '3D sound' via stereo /speakers/. This poses several issues: When you turn your head so the line connecting your ears is perpendicular to the line connecting the two speakers, the stereo effect goes away almost completely. If you turn your head less, the stereo effect is still being damped (which is bad, if you want the impression of 3D), but at least the sound sources don't move with your head (which is good, assuming you don't combine fixed position speakers with VR glasses without head tracking). Off course, because of the cross-talking mentioned in the video (which is almost negligible for headphones, but very present for speakers at fixed positions) you need very different mixing for speakers than for headphones, to get a comparable 3D illusion. That observation is not new, though. Actually I remember an infotainment application (a PC planetarium or interactive space object encyclopaedia or something like that) from the last century that had two modes for its (synthesized?) stereo sound, one for speakers and one for headphones. The sound there was 'just' music and some UI sounds (like when you click a button), so I'm not sure why that was important to the makers of the program, but it certainly gave the thing a very 'spacey' feeling. > You have the left signal, ls, and the right signal, rs. A filter computes > > rs_new = rs - ls > ls_new = ls - rs > > and then play rs_new and ls_new. (Details left as an exercise...) Dunno if it's a detail, but your equation are so oversimplified that they've become wrong (or useless, rather): With the computation above, you have rs_new = - ls_new. Duh. Now all spatial information is lost, you just have a mono signal on one speaker and its inversion on the other. (Which might further lead to funny destructive interference issues, when your distance to both speakers is exactly the same.) > In English---when you record in stereo, you record cross talk between > the mics which is recreated when you play back. This idea removes the > cross talk, and dramatically increases the 3D illusion. It is a > simple filter and works totally at playback time on all sound sources > and any stereo recording. It would be easy to add it to the viewer... If something like that is added, it has to be optional, or at least have a headphone and a speakers mode, so that headphone users aren't worse off than today. Cheers, Boroondas
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