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 (SPKR1, SPKR2) 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 (SPKR1, SPKR2); 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 (SPKR1, SPKR2) and the ambient audio sounds at the transducer (SPKR1, SPKR2); a controllable noise source for providing a noise signal; and a processing circuit that filters the reference microphone signal (ref) with a first adaptive filter to generate the anti-noise signal 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 noise shaping filter having a controllable frequency response that filters the noise signal to produce a frequency-shaped noise 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 (err) to provide the error signal (e), and wherein the processing circuit injects the frequency-shaped noise signal into an input to the secondary path adaptive filter and into the audio signal reproduced by the transducer (SPKR1, SPKR2) in place of or in combination with the source audio to cause the secondary path adaptive filter to continue to adapt when the source audio is absent or has reduced amplitude, and wherein the processing circuit analyzes the error signal (e) to determine frequency content of the error signal and adaptively controls the controllable frequency response of the noise shaping filter in conformity with the frequency content of the error signal (e) and further in conformity with at least one parameter of the secondary path response to reduce audibility of the noise signal in the audio signal reproduced by the transducer (SPKR1, SPKR2). an output for providing an output signal to an output transducer (SPKR1, SPKR2) 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 (SPKR1, SPKR2); 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 (SPKR1, SPKR2) and the ambient audio sounds at the transducer (SPKR1, SPKR2); a controllable noise source for providing a noise signal; and a processing circuit that filters the reference microphone signal (ref) with a first adaptive filter to generate the anti-noise signal 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 noise shaping filter having a controllable frequency response that filters the noise signal to produce a frequency-shaped noise 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 (err) to provide the error signal (e), and wherein the processing circuit injects the frequency-shaped noise signal into an input to the secondary path adaptive filter and into the audio signal reproduced by the transducer (SPKR1, SPKR2) in place of or in combination with the source audio to cause the secondary path adaptive filter to continue to adapt when the source audio is absent or has reduced amplitude, and wherein the processing circuit analyzes the error signal (e) to determine frequency content of the error signal and adaptively controls the controllable frequency response of the noise shaping filter in conformity with the frequency content of the error signal (e) and further in conformity with at least one parameter of the secondary path response to reduce audibility of the noise signal in the audio signal reproduced by the transducer (SPKR1, SPKR2).