A notch compensation apparatus and method comprising, based on input to and output from a notch filter, dynamically calculating a desired change to a notch frequency of the notch filter and specifying the desired change to the notch filter so as to cancel an input resonance of uncertain or time varying...http://www.google.com/patents/US6867642?utm_source=gb-gplus-sharePatent US6867642 - Realtime adaptive notch compensator
