Adaptive prediction differential PCM-type transmission apparatus and process with shaping of the quantization noise

A coding apparatus of the adaptive prediction differential PCM type, comprising a subtractor with two inputs receiving a sample of the signal to be coded y.sub.t and a prediction signal p.sub.t in which t is a sampling time and an output supplying an error signal e.sub.t, a quantizer of the error signal e.sub.t, followed by a coder of the quantized signal, a circuit able to form a restored error signal e.sub.t from the quantized or coded signal, an adder with two inputs receiving the restored error signal and the prediction signal p.sub.t and with an output supplying a restored signal y.sub.t and a predictor receiving the restored signals y.sub.t and e.sub.t and supplying the said prediction signal p.sub.t, said predictor comprising two linear filters, the first acting on the restored signal y.sub.t and comprising N circuits for the formation of coefficients A1.sub.t, A2.sub.t, . . . , AN.sub.t, a first group of N multipliers with two inputs respectively receiving N successive samples of y.sub.t to be filtered, i.e. y.sub.t, y.sub.t-1, . . . , y.sub.t-N+1 (or derived samples) and said N coefficients and an adder with N inputs connected to N multipliers of the first group and with an output supplying a prediction signal py.sub.t, the second comprising P circuits for the formation of P coefficients B1.sub.t, B2.sub.t, . . . , BP.sub.t and a second group of P multipliers with two inputs respectively receiving the P successive samples of e.sub.t, i.e. e.sub.t, e.sub.t-1, . . . , e.sub.t-P+1 and said P coefficients and an adder with P inputs connected to the P multipliers of the second group and with an output supplying a prediction signal pe.sub.t, said two filters comprising means for sequentially adjusting at each time t the coefficients A1.sub.t, . . . , AN.sub.t and B1.sub. t, . . . , BP.sub.t in such a way that the mean power of the error signal e.sub.t is minimal, wherein the predictor comprises means for shaping the spectrum of the quantization noise on y.sub.t (i.e. .DELTA.y.sub.t =y.sub.t -y.sub.t) by arranging said spectrum in parallel with that of the restored signal y.sub.t, said means comprising:

• (A) at least one of the following circuits:
• (a) a first circuit constituted by a filter of signal y.sub.t comprising a first group of N multipliers with two inputs respectively receiving N successive samples of y.sub.t, i.e. y.sub.t, y.sub.t-1, . . . , y.sub.t-N+1 (or derived samples) and N coefficients respectively equal to said coefficients A1.sub.t, A2.sub.t, . . . , AN.sub.t sampled in the first filter of the predictor acting on y.sub.t and an adding circuit with N inputs connected to the N multipliers of the first group and with an output supplying a filtered signal py.sub.t and by a first algebraic circuit with two inputs, one connected to the output of the filter of y.sub.t and receiving the signal py.sub.t and the other connected to the output of the filter of y.sub.t and receiving the signal py.sub.t, said first algebraic circuit supplying at one output a signal pAR.sub.t equal to .gamma..sub.AR py.sub.t +(1-.gamma..sub.AR) py.sub.t, in which .gamma..sub.AR is a regulatable coefficient between 0 and 1 (terminals included);
• (b) a second circuit constituted by a filter of the unquantized error signal e.sub.t comprising a second group of P multipliers with two inputs respectively receiving P successive samples of e.sub.t, i.e. e.sub.t, e.sub.t-1, . . . , e.sub.t-P+1 and P coefficients equal then respectively to said coefficients B1.sub.t, B2.sub.t, . . . , BP.sub.t sampled in the second filter of the predictor acting on e.sub.t and an adder with P inputs connected to P multipliers of the second group and with an output supplying a filtered signal pe.sub.t and by a second algebraic circuit with two inputs, one connected to the output of the filter of e.sub.t and receiving the signal pe.sub.t and the other to the output of the filter of e.sub.t and receiving the signal pe.sub.t, said second algebraic circuit supplying at an output a signal pMA.sub.t equal to .gamma..sub.MA pe.sub.t +(1-.gamma..sub.MA)pe.sub.t, in which .gamma..sub.MA is a regulatable coefficient between 0 and 1 (terminals included), the coefficients .gamma..sub.MA and .gamma..sub.AR not being simultaneously zero;
• (B) an adder with two inputs connected to the outputs of the first and second algebraic circuits and with an output supplying a signal pAR.sub.t +PMA.sub.t ;
• (C) a circuit with a delay of one sampling period with an input connected to the output of the adder and an output supplying the said prediction signal p.sub.t.