Telephone subscriber microphone and loudspeaker unit - suppresses acoustic and electrically transferred echo using comparator

摘要

A subscriber telephone station has a microphone (5) and loud-speaker (6) coupled through respective transmission and reception lines (1,2) and a differential coupler (3) to a telephone connection (4). Two echo suppression circuits suppress respectively the echo transferred electrically by the coupler (3) and acoustically by the microphone and loudspeaker. Each circuit monitors the mean signal power on both lines and controls a respective blocking circuit (7,9) in the transmission line (for acoustic echo) and reception line (for electrical echo), the suppression circuit for the former including a control circuit (8) which multiplies the reception mean signal level by a preset amount and the latter a control circuit (10) which multiplies the transmission mean signal level by the same amount. The control circuits then compare their respective mean signals and control the blocking circuits accordingly.