In most of the papers on crosstalk cancellation the point is made that at lower
freauencies the power required to cancel the bass becomes prohibitive. I will
make a feeble attempt to explain why this is a fallacy that derives from a
common propensity to rely soly on mathematics when using the HRTF functions
available.
Yes, if you assume that one needs to cancel crosstalk at 20Hz then the usual
HRTFs say the attenuation between the ears is negligible and so a high level
signal is needed to do any cancellation and then more energy is needed to
cancel this cancellation signal and the thing blows up.
But, the ear is not sensitive to crosstalk below say 100Hz so one needs to take
this into consideration. On can simply bypass bass frequencies around the HRTF
bsased canceller but it turns out this is not really necessary in HRTF-less
algorithms.
One basic premise of RACE is that no HRTF functions need be used. But let us
just concentrate on the bass region. RACE assumes a constant attenuation for a
signal reaching the wrong ear. As the frequency declines this assumption
becomes more and more inaccurate. But so what? What this means is that one is
not doing much cancellation as the frequency gets down to say 90Hz which is
okay since one does not localize well or at all at low bass frequencies
anyway. In other words the amount of cancellation automatically declines with
frequency so the overhead or power requirement does not change with
frequency either. The head room needed is the same at all the normal real
localization frequencies. (Very high frequencies are a different problem) You
can see this in a brief note by Angelo Farina comparing RACE with other XTC
methods. www.ambiophonics.org/papers/CrosstalkFilters.html
Ralph Glasgal
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