[LAU] Feedback Cancellation Plugin

[Fons Adriaensen]

On Sat, Oct 22, 2016 at 04:30:00PM +0200, Johannes Kroll wrote:
 
> I'm looking for a solution for adaptive feedback cancellation. The type
> of feedback that occurs between a microphone and speaker, not echo
> cancellation. Preferrably in the form of a plugin (LADSPA, LV2,
> DSSI, ...) or even as a standalone JACK app. This must be a common
> problem, but I haven't found a solution.

Because there isn't any that really works.

The basic reason is that the combined response of speaker, room
and mic in a typical PA situation is very irregular with hundreds
if not thousands of very narrow peaks, and the frequency of those
peaks is very sensitive to small movements of almost everything. 

Simple tricks like adaptive notch filters will maybe give you a dB
or so extra, but there it ends. 

The only thing that can work sometimes is shifting all frequencies
up or down by a few Hz, smoothing out the peaks. Simple to implement,
usable for speech but usually not for music because it will appear
to be out of tune.

One step beyond that is quasi proportional frequency shifting,
but that's quite complicated, has latency issues, and may also
affect music in ways that are not acceptable.

So in practice: use the right tools (mic, speakers), take room
acoustics into consideration when deciding on placement, and be
careful with EQ and effects. 

Ciao,

-- 
FA

A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)