[LAU] Feedback Cancellation Plugin

[Len Ovens]

On Sat, 22 Oct 2016, 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.

That would be because it requires a different solution every situation. 
What happens when the "fat lady" sings? The plugin nulls out her vocal 
thinking it is feedback. As happens, my acoustic instrument amp includes 
an anti-feedback section. It works in two parts:
polarity reversal
notch filter

The polarity of the FOH/monitor speakers does matter in this case. Piezo 
pickups are bad in this respect because the polarity may be different 
depending on mounting position (inside vs outside of sound plate). Mics 
_should_ be wired corectly and a FOH mixer/amp/speakers _should_ be too. 
Those are things to check. I have seen FOH mixers where the main outs are 
purposely 2- and 3+ for this reason. I don't know if this is standard or 
not.

Aim for as low of stage monitor level as possible. Setting mains level 
first may allow talent to use lower stage levels... but some are just 
deaf! In ear would be better in such a case. Note that I am using my 
(limited) experience with small venue work. A large venue is different.

Notch filters are the thing we think of first, but should probably be 
last. As already noted, this will not give you much more level and it does 
change the sound. The frequency to use changes with the hall, mic 
placement, talent mic know how, etc, etc. (teach your talent if they must 
hold the mic to hold it away from the capsule)

The other thought I have is that maybe you mean something to remove 
feedback noise on an already recorded file... notch filter is the tool for 
that... but it is really already too late by then.

--
Len Ovens
www.ovenwerks.net