[PD] feedback detection

[Charles Henry]

I've been working on the stable feedback between a loudspeaker and
microphone for a little while....and I'm still working on it.
I recommend first of all to try compression, as a means of reigning in
your unstable feedback.  Once the volume becomes loud enough, the
roll-off will decrease the loop gain to the point where it is no
longer unstable (won't blow up and clip persistently).  It will
however oscillate between low and high volumes this way.

To make your effects stable, you will need to do some analysis.  For
instance with convolution, you have to have the fourier components of
the convolving signal everywhere less than 1.  You are guaranteed
stability if the integral of the square of the signal is less than 1.
For instance with reverb effects, you can truncate your room reverb
signal at the point where the integral is less than 1 (or adjust the
gain by the integral of the signal)

The method I'm working on is for subband adaptive filtering to
equalize frequency response.  It's not going so well....I've been
trying a frequency domain algorithm for a little while now...and I've
tried a lot of different things to try to get it to converge, like
averaging and selection, with no good results yet.  Since I've already
got it to record 64 consecutive measurements, I will try to program an
independent components analysis next.

Chuck