FIELD: communication equipment, in particular, line estimation encoding using alternating rate code excitation. SUBSTANCE: rate detection logical circuit 14 provides choice of rate for encoding of voice signal. Rate choice depends on matched value of signal-to-noise ratio defined by unit 12 which calculates modes of normalized correlation function which is calculated by normalized self- correlation calculation unit 4. Also rate choice depends on zero level intersection sample, which is measured by zero level intersection counter 6, estimated amplification differential which is calculated by estimated amplification differential calculation unit 8, and power differential between frames, which is calculated by frame power differential calculation unit 10. EFFECT: optimal choice of encoding mode for increased efficiency of rate encoding of input voice signal. 22 cl, 2 dwg
