A method of generating an estimate of background noise in a playback environment, including steps of: during emission of sound in the playback environment, using a microphone to generate a microphone output signal, wherein the sound is indicative of audio content of a playback signal, and the microphone output signal is indicative of the audio content and background noise in the playback environment; characterized in generating gap confidence values in response to the microphone output signal and the playback signal, where each of the gap confidence values is for a different time, t , and is indicative of a confidence that there is a gap, at the time t , in the playback signal, wherein gap denotes a time or time interval of the playback signal at or in which playback content is missing or has a level less than a predetermined threshold, and wherein generating the gap confidence values includes generating a gap confidence value for each time, t , including by: processing the playback signal to determine a minimum in playback signal level for the time, t ; processing the microphone output signal to determine a smoothed level of the microphone output signal for the time, t ; and determining the gap confidence value for the time, t , to be indicative of how different the minimum in playback signal level for the time, t , is from the smoothed level of the microphone output signal for the time, t ; and generating an estimate of the background noise in the playback environment using the gap confidence values. during emission of sound in the playback environment, using a microphone to generate a microphone output signal, wherein the sound is indicative of audio content of a playback signal, and the microphone output signal is indicative of the audio content and background noise in the playback environment; characterized in generating gap confidence values in response to the microphone output signal and the playback signal, where each of the gap confidence values is for a different time, t , and is indicative of a confidence that there is a gap, at the time t , in the playback signal, wherein gap denotes a time or time interval of the playback signal at or in which playback content is missing or has a level less than a predetermined threshold, and wherein generating the gap confidence values includes generating a gap confidence value for each time, t , including by: processing the playback signal to determine a minimum in playback signal level for the time, t ; processing the microphone output signal to determine a smoothed level of the microphone output signal for the time, t ; and determining the gap confidence value for the time, t , to be indicative of how different the minimum in playback signal level for the time, t , is from the smoothed level of the microphone output signal for the time, t ; and generating an estimate of the background noise in the playback environment using the gap confidence values. processing the playback signal to determine a minimum in playback signal level for the time, t ; processing the microphone output signal to determine a smoothed level of the microphone output signal for the time, t ; and determining the gap confidence value for the time, t , to be indicative of how different the minimum in playback signal level for the time, t , is from the smoothed level of the microphone output signal for the time, t ; and generating an estimate of the background noise in the playback environment using the gap confidence values. <EOS>