[PD] feedback control

matthew jones mj at isvr.soton.ac.uk
Mon Mar 21 13:48:23 CET 2005

> if so multiply that bands which an adjustable value <1

but wouldn't that have weird effects when the signal you are attempting to
remove the feedback from is the sound of you whistling??
Or is this method the one that many feedback supressors use?  I thought it
was something like mimicking the effect of constantly moving the mic around
so that the frequencies at which the system is unstable actually move
around, done via slow variable delays or something like that.  Thats just a
guess though.

You could use an adaptive line enhancer, if it was feasible to regularly
calculate the inverse of a relatively large matrix and apply long FIR
filters... tho on a laptop this is maybe a bit too hopeful.

The true way would be to keep the mic fixed in place and measure the
response from loudspeakers to the mic, then calculate the optimal response
to cancel the signal as it arrives at the microphone with a second source
(maybe the right side of a stereo pair) and use an adaptive filter..... but
as Thomas says it would require near zero latency and heck, a lot of cpu

Any ideas/improvements anybody?


----- Original Message ----- 
From: "sven" <ml.sven at subscience.de>
To: <robertgarvin at bellsouth.net>; <pd-list at iem.at>
Sent: Sunday, March 20, 2005 8:45 PM
Subject: Re: [PD] feedback control

> hi robert,
> feedback suppression should be quite easy to achive w/ the vasp external.
> fft the incoming signal. check if there are 1 or 2 bands which are much
> louder than their neighbours.
> if so multiply that bands which an adjustable value <1 and than take the
> ifft.
> feedback noise is a pure sine (until it's getting so loud that it'
> distorts) so
> they don't have overtones and cause a significant peak in at most 2
> neighbouring bands.
> sven.
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