Patent US 4,123,620

An apparatus for controlling the generation of sound in the loudspeakers of intercommunicating telephone sets in response to pulse-code modulated speech signals from the microphones of the telephone sets. A digital comparator compares speech signals received from each microphone and delivers a binary control signal to a dividing circuit through which the speech signal having the highest maximum value passes. The dividing circuit responds to the control signal by dividing the speech signal by a desired factor. A loudspeaker, contained in the same telephone set as the microphone from which the speech signal having the highest maximum value emanated, is in circuit with a control unit. The same binary control signal causes the control unit to suppress the generation of sound in the loudspeaker.