Patent ID: 8611553

Claim:
A method of detecting instability in providing feedback-based active noise reduction (ANR) comprising monitoring audio that comprises feedback anti-noise sounds employed in providing the feedback-based ANR for a sound having a frequency within a predetermined range of frequencies and having an amplitude that at least meets a predetermined minimum amplitude, wherein the combination of the range of predetermined frequencies and the predetermined amplitude is associated with sounds indicative of instability, and monitoring audio that comprises feedback anti-noise sounds comprises: configuring a phase-locked loop (PLL) to lock onto a sound having a frequency within the predetermined range of frequencies and an amplitude at least meeting the predetermined minimum amplitude; monitoring audio to be acoustically output by an acoustic driver that comprises the feedback anti-noise sounds with the PLL; and awaiting an instance of the PLL locking onto a sound, further comprising routing the audio monitored by the PLL through a first high-pass filter, and routing the audio from the first high-pass filter through a summing node configured to subtract pass-through audio that has been routed through a second high-pass filter before providing the audio to the PLL.