Abstract: The invention discloses a method of reducing an interference noise signal fraction in a microphone signal, which method is based on estimating the interference noise signal fraction from a virtually pure interference noise signal and does not require any additional microphones. It is an essential feature of the method according to the invention that the signal which is used as a basis for estimating the interference noise signal fraction in the microphone signal of interest is received by means of one or more inversely operated loudspeakers. There is no need to install further microphones, particularly in situations where there are already one or more loudspeakers as components of an audio system. Such a situation arises for example in any motor vehicle fitted with an audio system.