System for control of speech direction in duplex telephone circuits

In apparatus for control of the speech direction in a duplex telephone system having at least a pair of stations interconnected by a single telephone line wherein each station includes a transmitting channel for transmitting a signal representative of the acoustic signals detected at the other channel at each station and includes a transmitting switch means for selectively connecting the transmitting channel to the telephone line, a receiving switch means for selectively connecting the receiving channel to the telephone line and duplex control means connected to the transmitting switch means and the receiving switch means for permitting only one of the channels to be connected with the telephone line to prevent feedback of signal from the receiving channel to the transmitting channel at each station;

• the improvement in which said duplex control means includes signal treating means connected to said transmitting channel for calculating and storing a regulating value dependent upon the envelope curve of the signal from the transmitting channel wherein the regulating value is equivalent to the factor by which the transmitting signal must be multiplied at any given time to be equal to the receiving signal when the transmitting signal is representative substantially of an acoustic feedback of the signal being received by the receiving channel, said signal treating means including means for adjusting the stored regulating value whenever said regulating value is changing at a rate which is less than a predetermined rate.