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 (SPKR) 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 (SPKR); a reference microphone input for receiving a reference microphone signal (ref) indicative of the ambient audio sounds; an error microphone input for receiving an error microphone signal (err) indicative of the acoustic output of the transducer (SPKR) and the ambient audio sounds at the transducer; and a processing circuit that adaptively generates the anti-noise signal from the reference microphone signal (ref) 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 (e) and the reference microphone signal (ref), 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 (err) to provide the error signal (e), wherein the processing circuit computes a ratio of a first indication of a magnitude of the error microphone signal including effects of the anti-noise signal to a second indication of the magnitude of the error microphone signal not including the effects of the anti-noise signal to determine an adaptive noise canceling gain, wherein the processing circuit compares the adaptive noise cancelling gain to a threshold gain value (THRES L, THRES H), wherein the processing circuit takes action on the anti-noise signal in response to determining that the adaptive noise canceling gain is greater than the threshold gain value, characterized in that the processing circuit filters the error signal with a first low-pass filter to generate the first indication of the magnitude of the error microphone signal, and wherein the processing circuit filters the reference microphone signal with a second low-pass filter to generate the second indication of the magnitude of the error microphone signal. an output for providing an output signal to an output transducer (SPKR) 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 (SPKR); a reference microphone input for receiving a reference microphone signal (ref) indicative of the ambient audio sounds; an error microphone input for receiving an error microphone signal (err) indicative of the acoustic output of the transducer (SPKR) and the ambient audio sounds at the transducer; and a processing circuit that adaptively generates the anti-noise signal from the reference microphone signal (ref) 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 (e) and the reference microphone signal (ref), 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 (err) to provide the error signal (e), wherein the processing circuit computes a ratio of a first indication of a magnitude of the error microphone signal including effects of the anti-noise signal to a second indication of the magnitude of the error microphone signal not including the effects of the anti-noise signal to determine an adaptive noise canceling gain, wherein the processing circuit compares the adaptive noise cancelling gain to a threshold gain value (THRES L, THRES H), wherein the processing circuit takes action on the anti-noise signal in response to determining that the adaptive noise canceling gain is greater than the threshold gain value, characterized in that the processing circuit filters the error signal with a first low-pass filter to generate the first indication of the magnitude of the error microphone signal, and wherein the processing circuit filters the reference microphone signal with a second low-pass filter to generate the second indication of the magnitude of the error microphone signal.