Audio signal processing apparatus

The signals from a plurality of microphones 5-1,5-2,5-3 are analysed to determine the direction of one or more sound sources. The relative times of arrival of a sound at each microphone are determined and used, in conjunction with the relative positions of the microphones, to estimate the direction of the or each sound source, e.g. a talker 1-1,1-2,1-3 at a meeting table or a musical instrument in a group. Knowledge of the direction of each sound source can be used to separate the signals corresponding to the sources, e.g. for recording or transcribing. As shown, the signals from each microphone are Fourier transformed and stored as separate spectrograms 31-1,31-2,31-3 in a buffer 29. The spectrograms are then processed in a module 33 to determine the number and direction of sound sources, from a knowledge of which separate spectrograms 37-1,37-2,37-3,37-N for the respective sound sources can be derived.