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: an adaptive filter having a response that generates the anti-noise signal from the reference microphone signal (ref) to reduce the presence of the ambient audio sounds heard by the listener; and a coefficient control block that shapes the response of the adaptive filter in conformity with the error microphone signal (err) and the reference microphone signal (ref) by adapting the response of the adaptive filter to minimize the ambient audio sounds in the error microphone signal (err); a coefficient bias control block which is configured to control the response of the adaptive filter towards zero in a range of frequencies by biasing coefficients of the coefficient control block, wherein the coefficient bias control block is configured to inject a noise signal within the range of frequencies into the coefficient control block to bias coefficients of the coefficient control block by causing the coefficient control block to shape the response of the adaptive filter in conformity with the error microphone signal (err) combined with the noise signal and the reference microphone signal (ref) combined with the noise signal, characterized in that the coefficient bias control block comprises a noise source for generating a white noise signal and a bandpass filter for filtering the white noise signal within the range of frequencies to generate the noise signal; wherein the range of frequencies is outside of a frequency content of the source audio 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 an adaptive filter having a response that generates the anti-noise signal from the reference microphone signal (ref) to reduce the presence of the ambient audio sounds heard by the listener; and a coefficient control block that shapes the response of the adaptive filter in conformity with the error microphone signal (err) and the reference microphone signal (ref) by adapting the response of the adaptive filter to minimize the ambient audio sounds in the error microphone signal (err); a coefficient bias control block which is configured to control the response of the adaptive filter towards zero in a range of frequencies by biasing coefficients of the coefficient control block, wherein the coefficient bias control block is configured to inject a noise signal within the range of frequencies into the coefficient control block to bias coefficients of the coefficient control block by causing the coefficient control block to shape the response of the adaptive filter in conformity with the error microphone signal (err) combined with the noise signal and the reference microphone signal (ref) combined with the noise signal, characterized in that the coefficient bias control block comprises a noise source for generating a white noise signal and a bandpass filter for filtering the white noise signal within the range of frequencies to generate the noise signal; wherein the range of frequencies is outside of a frequency content of the source audio signal.