22 In an echo cancelling device comprising an echo canceller 13 for producing, in response to a send-in signal SIN and a receive-in signal RIN, a residual signal RES in which an echo signal ECHO is cancelled, a residual echo level estimator 106 estimates, in response to the residual signal, a residual echo level in the residual signal and produces a threshold signal THR with a threshold level equal to the residual echo level. Responsive to the receive-in, the residual, and the threshold signals, a residual echo suppressor 105 produces a send-out signal SOUT with a residual echo adaptively suppressed in response to the threshold level. Preferably, the echo canceller comprises an echo estimating circuit 131 which estimates an echo estimation signal in response to the receive-in and the residual signals. A subtracter 132 subtracts the echo estimation signal from the send-in signal and produces the residual signal. Responsive to the send-in and the receive-in signals, a communication state detector 14 produces an inhibit signal INH when a level of the receive-in signal is greater than that of the send-in signal. The inhibit signal prevents the echo estimating circuit from producing the echo estimation signal and makes the residual echo level estimator keep the threshold level at the residual echo level estimated immediately before the inhibit signal is produced.
ECHO CANCELLER WITH ADAPTIVE SUPPRESSION OF RESIDUAL ECHO LEVEL