Frequency and direction-dependent ambient sound handling in personal audio devices having adaptive noise cancellation (ANC)

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

• measuring the ambient audio sounds with a reference microphone to generate a reference microphone signal;
• measuring an acoustic output of a transducer and the ambient audio sounds with an error microphone to generate an error microphone signal;
• adaptively generating an anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener using an adaptive filter having a response controlled by coefficients computed by a coefficient control block having a first input receiving a first signal derived from the reference microphone signal and a second input receiving a second signal derived from the error microphone signal;
• combining the anti-noise signal with source audio;
• providing a result of the combining to the transducer;
• analyzing the reference microphone signal to detect ambient sounds and determine one or more frequencies or frequency bands in which the ambient sounds have energy;
• and
• altering adaptation of the response of the adaptive filter in response to the detection of the ambient sounds and in conformity with a result of determining the one or more frequencies or frequency bands by altering frequency content of either the first signal or the second signal to reduce a sensitivity of adaptation of the response of the adaptive filter to the detected ambient sounds.

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;
• 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 generates the anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener using an adaptive filter having a response controlled by a coefficient control block having a first input receiving a first signal derived from the reference microphone signal and a second input receiving a second signal derived from the error microphone signal, wherein the processing circuit analyzes the reference microphone signal to detect ambient sounds and determine one or more frequencies or frequency bands in which the ambient sounds have energy, and wherein the processing circuit alters adaptation of the response of the adaptive filter in response to the detection of the ambient sounds and in conformity with a result of determining the one or more frequencies or frequency bands by altering frequency content of either the first signal or the second signal to reduce a sensitivity of the adaptation of the response of the adaptive filter at the one or more frequencies or frequency bands.