Ear-coupling detection and adjustment of adaptive response in noise-canceling in personal audio devices

A method of canceling ambient audio sounds in the proximity of a transducer of a personal audio device, the method comprising:

• first measuring ambient audio sounds with a reference microphone;
• second measuring an output of the transducer with an error microphone;
• adaptively generating an anti-noise signal from a result of the first measuring for countering the effects of ambient audio sounds at an acoustic output of the transducer by adapting a response of a first adaptive filter that filters an output of the reference microphone;
• filtering the reference microphone signal to generate the anti-noise signal,
• shaping the source audio with a secondary path response;
• removing the shaped source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise signal and ambient audio sounds delivered to the listener;
• adapting the response of the first adaptive filter to minimize the error signal;
• combining the anti-noise signal with a source audio signal to generate an audio signal provided to the transducer;
• determining a degree of coupling between the transducer and an ear of the listener;
• detecting a change in the degree of coupling by comparing a value of an ear pressure indication computed from the secondary path response to a predetermined threshold;
• and
• altering the response of the first adaptive filter in response to the value of the ear pressure indication crossing the predetermined threshold.

An integrated circuit for implementing at least a portion of a personal audio device, comprising:

• an output for providing a signal to a transducer including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer;
• a reference microphone input for receiving a reference microphone signal indicative of the ambient audio sounds;
• an error microphone input for receiving an error microphone signal indicative of the output of the transducer;
• and
• a processing circuit that implements a first adaptive filter having a response that shapes the anti-noise signal to reduce the presence of the ambient audio sounds heard by the listener listener, wherein the first adaptive filter filters the reference microphone signal to generate the anti-noise signal, wherein the processing circuit implements a secondary path adaptive filter having a secondary path response that shapes the source audio and a combiner that removes the shaped source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise signal and ambient audio sounds delivered to the listener, wherein the processing circuit adapts the response of the first adaptive filter to minimize the error signal, wherein the processing circuit determines a degree of coupling between the transducer and an ear of the listener and detects a change in the degree of coupling by comparing a value of an ear pressure indication computed from the secondary path response to a predetermined threshold, and wherein the processing circuit alters the response of the first adaptive filter in response to the value of the ear pressure indication crossing the predetermined threshold.