Abstract: The present invention features an ADPCM decoder of the instantaneous companding type which comprises two memory circuits (each preferably PROM). The first memory contains a plurality of differential values and the second a plurality of step size control codes. The memories receives ADPCM input codes which function as address signals. The memories are connected through an adder and a shift register feedback connected with the adder. The first memory receives two inputs, one of which is an ADPCM input code and the other is an input consisting of the sum of the current output of the second memory plus the previous value outputted thereby. The first memory produces a differential value on the basis of the two inputs applied.

Abstract: There is disclosed a system for the extraction of pole parameter values. The system comprises an autocorrelation value calculating circuit receiving an input voice signal through a time window, for calculating an autocorrelation value V.sub.i (i=0, 1, 2, . . .) of the input voice signal within the time window; a linear prediction coefficient memory circuit for storing linear prediction coefficients (.alpha..sub.1, .alpha..sub.2) corresponding to various pole parameter values; a signal processor for receiving as its input the output value V.sub.i of the autocorrelation value calculating circuit, performing thereon an arithmetic operation according to the following formula using the prediction coefficients (.alpha..sub.1, .alpha..sub.2) supplied by the linear prediction coefficient memory circuit:r.sub.i =(l+.alpha..sub.1.sup.2 +.alpha..sub.2.sup.2)V.sub.i -(.alpha..sub.1 -.alpha..sub.1 .alpha..sub.2)V.sub.i+1 -(.alpha..sub.1 -.alpha..sub.1 .alpha..sub.2)V.sub.i-1 -.alpha..sub.2 V.sub.i-2 -.alpha..sub.2 V.sub.