On Wed, Jun 01, 2011 at 08:59:30PM +0100, dw wrote: > Computer say " i can give you itd=450us @ 20Hz" off the shelf. That is > very near field, so should be unaffected by the room. I don't know > whether it is true..
It depends on what you start from. If you have an intensity (panned) stereo LF source at e.g. 30 degrees left (so only in the L channel, assuming a normal stereo triangle), then reproducing this using two speakers at +/- 7.5 degrees is easy. It only requires a difference channel (L-R) gain 13 dB or so higher than the sum (L+R) gain, and independent of frequency. Some power is wasted but it will work. Things are different when starting with a binaural signal for for the same source. This will require a very high difference channel gain (proportional to 1/f, and complex), much more than could ever be used in practice. The whole concept of Ambiophonics is based on the idea of delivering the L,R signals in a stereo recording to the respective ears without crosstalk to the other. The basic assumption is that the signals are binaural. But for that kind of signal it can't work for low frequencies because it would require much more L-R gain than is possible in practice. If it works, and it does in many cases, it is because most recordings are *not* binaural to start with, but a mix of intensity based stereo (at LF) with *some* ITD at mid and high frequencies. For example the popular ORTF technique will deliver exactly that. For a pure binaural recording, Ambiophonics fails at LF. For a pure intensity (panned) stereo one, it will fail at mid and high frequencies because there is no ITD in the recorded signal (normally spaced speakers would create the ITD at playback). It Ambiophonics works well for some recordings it it just because these are intensity based at LF (requiring only moderate L-R gain), while still having some ITD at mid and high frequencies. Presenting it as a system that delivers binaural signals to the respective ears without crosstalk is misleading, that is *not* why it works in practice. Ciao, -- FA _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
