[PD] feedback control

[sven]

hi robert,
feedback suppression should be quite easy to achive w/ the vasp external.
fft the incoming signal. check if there are 1 or 2 bands which are much 
louder than their neighbours.
if so multiply that bands which an adjustable value <1 and than take the ifft.
feedback noise is a pure sine (until it's getting so loud that it' distorts) so
they don't have overtones and cause a significant peak in at most 2 
neighbouring bands.

sven.