The echo compensator (2) introduced between two PCM subscriber network connections (1,3) consists of a subtractor (9) and a transversal filter (10). For test purpsoes it is connected (19-21) to equipment (14) which includes an amplitude generator (17) producing 7-bit amplitude values for the transmission and reception channels (4,5) and a pseudo-random sign generator (16) comprising nine D flip-flops and an Exclusive-OR gate. A transit time device (15) comprises four D flip-flops clocked at 8 kHz. An amplitude value monitor (18) ascertains whether the amplitude at the output of the transmission channel (4) after a predetermined delay following the application of the test signal has declined to a residual value.
