MIC covering detection in personal audio devices

A method of preventing production of erroneous anti-noise in a personal audio device having adaptive noise canceling, the method comprising:

• producing an acoustic output with a transducer, the acoustic output including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in the proximity of an acoustic output of the transducer;
• first measuring the ambient audio sounds with a first microphone of a plurality of microphones to generate a first microphone signal;
• generating the anti-noise signal from the first microphone signal with a first adaptive filter;
• second measuring the ambient audio sounds with second microphone of the plurality of microphones to generate a second microphone signal;
• first detecting a first amplitude of the first microphone signal to generate a first microphone level signal;
• second detecting a second amplitude of the at least one second microphone signal to generate at least one second microphone level signal;
• first comparing the first microphone level signal and a signal level of one of the plurality of microphones other than the first microphone to determine a first differences between the first microphone level signal and the signal level of the one of the plurality of microphones other than the first microphone;
• determining whether the first microphone is at least partially obstructed from a result of the first comparing;
• first taking action in response to determining that the first microphone is at least partially obstructed, by halting adaptation of the first adaptive filter so that first coefficients of the adaptive filter are maintained at their existing values to prevent the anti-noise signal from being generated erroneously;
• second comparing the second microphone level signal and a signal level of one of the plurality of microphones other than the second microphone to determine a second differences between the second microphone level signal and the signal level of the one of the plurality of microphones other than the second microphone;
• determining whether the second microphone is at least partially obstructed from a result of the second comparing;
• and
• second taking action in response to determining that the second microphone is at least partially obstructed, by halting adaptation of the first adaptive filter and the second adaptive filter and resetting the first coefficients and the second coefficients to predetermined values.

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 first microphone input of a plurality of microphone inputs for receiving a first microphone signal indicative of the ambient audio sounds from a first microphone;
• a second microphone input of the plurality of microphone inputs for receiving a second microphone signal indicative of the ambient audio sounds from a second microphone;
• and
• a plurality of microphones, including a first microphone mounted on the housing that, when unobstructed, provides a first microphone signal indicative of the ambient audio sounds, wherein a second microphone of the plurality of microphones is mounted on the housing and that, when unobstructed, provides a second microphone signal indicative of the ambient audio sounds;
• and
• a processing circuit that implements a first adaptive filter having a response that generates the anti-noise signal from the first microphone signal, a second adaptive filter for generating shaped source audio from the source audio and a combiner for removing the shaped source audio from the second microphone signal to generate an error signal provided to a coefficient control block that controls coefficients of the first adaptive filter, wherein the processing circuit implements a first signal level detector for detecting a first amplitude of the first microphone signal to generate a first microphone level signal and second signal level detector for detecting a second amplitude of the second microphone signal to generate a second microphone level signal, and wherein the processing circuit further compares the first microphone level signal and a signal level of one of the plurality of microphone inputs other than the first microphone input and, in response to determining that a first differences between the first microphone level signal and the signal level of the one of the plurality of microphone inputs other than the first microphone input indicates that the first microphone is at least partially obstructed, halts adaptation of the first adaptive filter so that first coefficients of the first adaptive filter are maintained at their existing values to prevent the anti-noise signal from being generated erroneously, and wherein the processing circuit compares the second microphone level signal and a signal level of one of the plurality of microphones inputs other than the second microphone input, and in response to determining that a second differences between the second microphone level signal and the signal level of the one of the plurality of microphone inputs other than the second microphone input indicates that the second microphone is at least partially obstructed, halts adaptation of the first adaptive filter and the second adaptive filter and resets the first coefficients and the second coefficients to predetermined values.