[PD] Re: [PD-ot] how low (latency) can you go?

[Charles Henry]

I use the cc~ external.  The time domain function is not so efficient
for large sizes, since it's an O(N^2) algorithm.  The freq domain
version uses a fourier algorithm, so it uses only O(N*log(N)).
use [cc~ 1024] for time-domain where +/- 1024 is the bounds of the cc~
use [cc~ f] for one-block at a time measurements in freq. domain
and [cc~ r] for running frequency domain cc~
the frequency domain stuff is actually a cross-covariance, rather than
cross-correlation.
The peak you get from cc~ will not be very clearly defined, because
the loudspeaker has reactive elements, phase shifts, etc....
I'm still thinking about the normalization routine to turn the
cross-covariance into a cross-correlation (it doesn't matter if all
you're looking for is a peak).  I'm not sure how to do it yet
I would suggest using the running cc~ with a large enough block size
to cover the latency and sound sources that are much much longer than
that.
You'll probably have to get the latest version from Jamie's flib CVS directory
http://pure-data.cvs.sourceforge.net/pure-data/externals/postlude/flib/src/
The "zero" location is blocksize/2, so whatever result you get for the
peak, you'll want to subtract blocksize/2.

Chuck
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