An integrated circuit for implementing at least a portion of a personal audio device, comprising: an output for providing a signal to a transducer (SPKR) including both a source audio signal for playback to a listener and an anti-noise signal for countering the effect 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 output of the transducer (SPKR) and the ambient audio sounds at the transducer (SPKR); and a processing circuit that implements: at least one of: a feedback filter (32, 44) having a response that generates at least a portion of the anti-noise signal from a playback corrected error; and a feedforward filter having a response that generates at least a portion of the anti-noise signal from the reference microphone signal; the processing circuit further implementing a secondary path estimate filter configured to model an electro-acoustic path of the source audio signal and having a response that generates a secondary path estimate signal from the source audio signal by filtering the source audio signal with the secondary path estimate filter; and a secondary path estimate performance monitor configured to monitor performance of the secondary path estimate filter in modeling the electro-acoustic path by comparing the error microphone signal (err) to the playback-corrected error (PBCE), the playback corrected error (PBCE) being based on a difference between the error microphone signal (err) and the secondary path estimate signal. an output for providing a signal to a transducer (SPKR) including both a source audio signal for playback to a listener and an anti-noise signal for countering the effect 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 output of the transducer (SPKR) and the ambient audio sounds at the transducer (SPKR); and a processing circuit that implements: at least one of: a feedback filter (32, 44) having a response that generates at least a portion of the anti-noise signal from a playback corrected error; and a feedforward filter having a response that generates at least a portion of the anti-noise signal from the reference microphone signal; a feedback filter (32, 44) having a response that generates at least a portion of the anti-noise signal from a playback corrected error; and a feedforward filter having a response that generates at least a portion of the anti-noise signal from the reference microphone signal; the processing circuit further implementing a secondary path estimate filter configured to model an electro-acoustic path of the source audio signal and having a response that generates a secondary path estimate signal from the source audio signal by filtering the source audio signal with the secondary path estimate filter; and a secondary path estimate performance monitor configured to monitor performance of the secondary path estimate filter in modeling the electro-acoustic path by comparing the error microphone signal (err) to the playback-corrected error (PBCE), the playback corrected error (PBCE) being based on a difference between the error microphone signal (err) and the secondary path estimate signal.