Abstract: A speakerphone system has a speaker and microphone in a common acoustic environment and electrically preceded and succeeded, respectively, by receive and transmit sections and adapted, respectively, to reproduce as sounds by such speaker signals passed through such receive section from a remote station, and to convert sounds sensed by such microphone into signals passed through such transmit section to such station. A computer derives from the signals from the microphone an electric quantity which is a measure of the average audible ambient noise level in such environment, and the computer uses such quantity as one factor among others in switching signal losses between such two sections so as to change the state of operation of the system between transmit and receive states.