Downlink tone detection and adaptation of a secondary path response model in an adaptive noise canceling system

A method of countering effects of ambient audio sounds by a personal audio device, the method comprising:

• adaptively generating an anti-noise signal from the reference microphone signal by adapting a first adaptive filter to reduce the presence of the ambient audio sounds heard by the listener in conformity with an error signal and a reference microphone signal;
• combining the anti-noise signal with source audio;
• providing a result of the combining to a transducer;
• measuring the ambient audio sounds with a reference microphone;
• measuring an acoustic output of the transducer and the ambient audio sounds with an error microphone;
• implementing a secondary path adaptive filter having a secondary path response that shapes the source audio and a combiner that removes the source audio from the error microphone signal to provide the error signal;
• detecting a frequency-dependent characteristic of the source audio that is independent of The ambient audio sounds using frequency-selective filtering of the source audio;
• and
• taking action to prevent improper generation of the anti-noise signal in response to detecting the characteristic of the source audio.

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

• an output for providing an output signal to an output 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 acoustic output of the transducer and the ambient audio sounds at the transducer;
• and
• a processing circuit that adaptively generates the anti-noise signal from the reference microphone signal by adapting a first adaptive filter to reduce the presence of the ambient audio sounds heard by the listener in conformity with an error signal and the reference microphone 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 source audio from the error microphone signal to provide the error signal, wherein the processing circuit detects a frequency-dependent characteristic of the source audio that is independent of the ambient audio sounds using frequency selective filtering of the source audio and takes action to prevent improper generation of the anti-noise signal in response to detecting the characteristic of the source audio.