On Mon, Jun 13, 2011 at 12:13:19AM +0200, Franck M. wrote: > I'm not sure if I understood the whole mathematical formalism in there, but > Choueiri states that BACCH filters end up maximizing out-of-phase response > in low range (the so-called "first band"), and as a consequence in-phase > response will be something like -20 or -30dB lower. > > So eventually a mono bass, ie. totally in phase, would simply be cancelled > out. I suspect Choueiri's filters will work well for typical bass sounds > only if the XTC is bypassed for low frequencies.
There is no reason why an XTC system should remove center bass signals, and as far as I know none of them do this. I suspect you are confusing 'out-of-phase' and 'difference'. In a recording using binaural or similar techniques, a non-centered bass signal will have almost the same amplitude in L and R, and there will just be a small phase difference between L and R (which is also the only directional info available). This is what is expected at the ears, and it will work perfectly e.g. when listening on headphones. For such a signal, the difference L-R is very small. Reproducing it correctly using normally spaced stereo speakers (which requires amplitude differences instead, this recreates the original signals at the ears) means you need high gain for this L-R signal. To reproduce it (and create an off-center bass) using closely spaced speakers and crosstalk cancellation requires even more. But none of this means that a mono (center) bass would be removed. The real problem with XTC systems is that in practice they can't reproduce off-center bass in the correct direction. It could be done in theory but the required gain for the difference signal is so high that you would blow up the speakers if the input is amplitude based stereo and contains off-center bass. Or if you would just disconnect one input. So what's done is to limit this gain, which means reverting to mono at LF. Ciao, -- FA _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
