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.