Image Number 3 for United States Patent #5305243.
A device compares two variable analogue signals, e.g. varying in time, such as audio or video signals. The signals, which are either different or identical but shifted in time, are within a predetermined frequency range. The device includes two parallel channels for processing analogue signals. One of the channels introduces a time shift of one signal with respect to the other, the shift being equal to a 1/4 period at the center frequency of the band. Both channels include in series circuits for transforming the analogue signals into binary logic signals, a logic circuit, a summing circuit for establishing a first and second correlation signal. An adder adds the absolute values of the first and second correlation signals to form a third correlation signal that is substantially independent of any time shift between the analogue signals.