d represents the distance between the microphones 1 a and 1 b c sound velocity and u03c6 the angle between the direction 3 of sound approaching and the connection line 2 between the microphones 1 a and 1 b block 4 represents a discrimination unit to which signals f t and r t are sent the outputs of the discrimination circuit 4 are designated f t and r t the amplitude of f t and r t depends on angle u03c6 wherein a cardioid pattern is obtained for example that means that the amplitude a of signals f and r corresponds to equation 2 a a 0 2 u2062 1 cos u2062 u2062 u03c6 2 a 0 represents the maximum amplitude obtained if the source of sound is on the connection line 2 between microphones 1 a and 1 b which means that the maximum amplitude of f t is at u03c6 0 and of r t at u03c6 u03c0 signals f t and r t are processed further in the processing unit 5 the output of which is designated with ff t and rr t in fig2 the discrimination unit 4 is explained further the first signal f t is sent into a first subtractor 6 a the output of which is delayed in a delaying unit 7 a for a predetermined time t 0 signal r t is sent to a second subtractor 6 b the output of which is sent to a second delaying unit 7 b which.