Abstract: The speech/silence discriminator is used on a telephone line to distinguish between periods of speech and periods of silence. A signal derived from the speech signal is, in the speech state compared to an adaptive threshold which is a fraction of the maximum, to be eventually quantized, reached by said signal during the period of speech which is considered; the speech to silence transition being determined when the signal decreases below said threshold level, the threshold level being determined during each speech period as a function of the maximum attained during the period. The adaptive threshold has a minimum value of -60 dBm. It is also comprised of a noise level evaluation circuit which determines the threshold decision level (.gtoreq.-60 dBM) for the transition from silence to speech which once reached, in the period of silence, enables the discriminator to go from the silent state to the speech state. It is useable in speech interpolation systems.