Patent ID: 8824695

Claim:
A feedback based active noise reduction system comprising: a feedback element including a first signal input for accepting an input signal, a feedback input for accepting a first feedback signal from a first sensor, a control input for accepting a control parameter for adjusting a gain characteristic and a phase characteristic of the feedback element, and a driver output for providing a driver signal to a driver; and an instability detector for detecting an instability condition including the presence of an oscillation in a specified frequency range in the feedback element and forming the control parameter based on a result of the detection, the instability detector including a second signal input for accepting the input signal, a driver input for accepting the driver signal, a control parameter output for providing the control parameter to the control parameter input of the feedback element, and a plurality of inputs for accepting a plurality of feedback signals from a plurality of sensors including the first sensor, wherein detecting the instability condition includes processing the plurality of feedback signals to determine a characteristic of an acoustic path between the driver and the first sensor, and determining a characteristic of the feedback element based on the input signal and the driver signal including analyzing the input signal and driver signal to determine whether the oscillation is present in the driver signal and that the oscillation is not present in the input signal.