US Patent 9922636 Mitigation of unstable conditions in an active noise control system

The technology described in this document can be embodied in a computer-implemented method that includes receiving a portion of a feedback signal of an active noise control (ANC) system, and processing the portion of the feedback signal using an adaptive line enhancer (ALE) filter to detect a tonal signature. The method also includes determining, by one or more processing devices, that the tonal signature represents an unstable condition, and responsive to determining that the tonal signature represents an unstable condition, generating one or more control signals for adjusting one or more parameters of the ANC system, to mitigate the unstable condition.