[PD] microphone feedback canceling

[tim]

Hi,
I'm planning to use a microphone on stage, with pd.
With it comes the risk of unwanted feedback.
Has anyone done a feedback canceling patch or seen a proven technique ?
I don't know much about how this works in commercial devices (and if 
they really work for that matter), but I suppose it's done by detecting 
a frequency that peaks and apply a filter on that...

Tim