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how to prevent a feedback?

October 26, 2009 | 1:08 pm

Is it possible to prevent feedback in Live Concert?
I had a small concert in a local for cello and live electronic.
Cello player had to play before a subwoofer.
Is there any possibility to prevent a feedback?
I built a band reject filter.
But, it does not work.

best,
prko


October 26, 2009 | 1:30 pm

preventing feedback in a live show is always hard, but is mostly soprted by a good placement of microphones from the monitors/speakers.

as with feedback the noise goes from the speakers and back through the microphone, and back through the speakers then through the microphone again, all until someone turns things down or by moving the microphone itself.
also as well, if microphones are just sitting near them as well, and even if a sound comes out, it can spell disaster.

having things like filters is good, but does not always work. the same is also with eq, it can, but also can not work.
a lot of the culprit as to why is also based on the shape of the room, if it is just a plain wooden floor and so on and so forth.

one thing i used to do to really try and stop feedback and any form of noise at a new venue to play or set up for playing, is i always get there a few hours before so as to find problems, if any.
a lot of times it is just because microphones and speakers are just too high in volume.
it also can depend on how sensitive the microphone can be.
the one reason shure sm57/58 microphone are one of the best stage/studio microphones is because it deals with sound that is right next to them [i can not remember the correct term right now] plus are cheap.

my one thing i would suggest is look at where your microphones are placed compared to your speakers, how far are they apart etc.
a lot of the times, feedback can happen because the speakers at small venues are just way too big so the microphones pick up what is being played.
if placed in the wrong place, you can just get a dirty screaming sound.
also eq never hurts to try as well.

hope this helped…


October 26, 2009 | 2:09 pm

If you want to do this in Max you can try to look at filtergraph~ & biquad~ comBined with some sort of a pitch detection. But of course, a notch filter will also filter out wanted musical frequencies.

I’m doing a installation now, with fixed placement of mics and speakers. A quick fix for blasting waves of feedback, was to average the amplitude on the mic inputs. If the averaged value (using slide) climb above a chosen threshold, it routes the audio into a sidepath with a pretty radical filter. I use Tristan Jehan’s pitch~-external to set the center frequency of a biquad~. I modulate this frequency a bit with a LFO.

This system is not working great, and I guess the trigger should be something like: If a detected frequency is stable for x seconds, with rising amplitude – assume it’s feedback and turn on the antifeedback filter until the amplitude of that frequency has diminished below a certain treshold.


October 30, 2009 | 8:54 pm

Thanks!

Yes, the microphone is very important to prevent a feedback.
MY question is for any urgent case….

I have tried with [fffb~] and [analyser~].
I had no success.

I will report when I have success with a patch!

best,
prko


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