Abstract: An interface circuit between a four wire line and a two wire line includes correlator and control circuit means connected for receiving a longitudinal signal (V.sub.1) and a transversal signal (V.sub.t) corresponding to a differential signal received on the terminals of a two wire interface from the two wire line. The correlator and control circuit includes a circuit for creating a correction signals being a measure of the correlation between the longitudinal signal and the transversal signal. The circuit for creating the correction signal is connected for using this correction signal to adaptively control the amplifications in feed back loops so as to minimize the correlation between the longitudinal and transversal signals.