[PD] feedback control

Spencer Russell Spencer.Russell at oberlin.edu
Mon Mar 21 16:41:01 CET 2005

On Mon, Mar 21, 2005 at 12:48:23PM +0000, matthew jones wrote:
> 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.
> Any ideas/improvements anybody?
I can tell you how live sound guys get rid of feedback. As long
as the Mics are stationary, the feedback resonances don't change
throughout the gig, so before the performance, part of a live
sound engineer's setup is "ringing out" the venue. Basically, you
just turn up the main volume until you start to hear feedback,
then back down a little, then you turn up each band on a graphic
EQ unit(Those things with 15 or 31 sliders, each representing a
narrow band of frequencies) and find out where the first resonance
is, and bring that band down some, which allows you to bring the
mains up higher, until you run into another feedback area, so
then you repeat the process of finding the resonant frequency and
bringing it down, bringing the mains up even higher. This doesn't
work quite as well if the mics are moving around, but it
definently still helps.

looking at the manual on the behringer page, it looks like these
feedback supressors basically do the same thing, and require
"training" at the beginning of the gig. They basically just
simplifiy the process of locating the feedback frequencies. I
would worry about putting any behringer DSP in my signal chain.
I've got this little behringer mixer(cause it's cheap) and not
only is there strange bleed from the effects bus, the DSP effects
are horrendously noisy.


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