Abstract: A loudspeaking telephone has a differential coupler (3) connecting a two-way two-wire telephone line (4) to separate transmission and reception channels (1 and 2 respectively) including respectively a microphone (5) and a loudspeaker (7). A first transversal filter (10) synthesizes an acoustic echo signal ya which is subtracted from the microphone signal to deliver a substantially echo-free signal to the transmission channel. Likewise a second transversal filter (11) synthesizes an electrical echo signal to deliver a substantially echo-free signal to the reception channel.

Abstract: Centering device for an adjustable transverse filter of a digital echo canceller in a telephone network, in which said transverse filter produces samples of a synthetic echo signal y (t) deduced from N servo-controlled weights C representing the samples of the pulse-response of the echo path and deduced from the same number of samples X (T) of a signal x (t) in the reception line, and in which the N samples X (T) are delayed in a delay circuit ahead of said transverse filter, the delay time being given by the minor rank of said coefficients C lying above a threshold value, this minor rank being detected at the end of given convergence time of said transverse filter.

Abstract: Echo canceller, canceling an echo signal y (t), generated by a signal x (t), comprising a transversal digital filter whose N weighting coefficients C.sub.i, correlated with N coded samples of x (t) enable the forming of a synthetic echo signal y (t) and comprising an adaptive control loop adjusting the coefficients C.sub.i, characterized in that the adaptive control loops effects the correlation between the signs of the N coded samples of x (t) and of the residual echo signal .gamma. (t) and determines the correction .DELTA. C.sub.i adjusting the coefficients C.sub.i by multiplication of the residual signal .vertline. .epsilon. (t) .vertline. by a coefficient .alpha. close to zero accompanied by the sign of the aforementioned correlation of signs.