| 摘要 |
PURPOSE:To reduce rasping noise, by coding and sending estimated remainder signals with the N.B-number of quantization bits in a ratio of one to N-number of sample periods(N is integer>=2). CONSTITUTION:The output pulse of a pulse generation circuit 1, after being quantized to the NB-number of quantization bits per sample by a quantizer 2, is supplied to a synthesizing circuit 5 consisting of a linear estimation synthesizing filter, and is generated as a reproduced voice. The reproduced voice is supplied to a differentiator 6, and a difference between an original voice signal is taken, and is generated as the estimated remainder signal, and after that, it is supplied to a pulse amplitude control circuit 8. The amplitude of the output pulse of the pulse generation circuit 1 is controlled so as to set a coded error after a time nT at a minimum level by the output signal of the pulse amplitude control circuit 8. At this time, an M-order digital filter is provided at the input stage of the synthesizing circuit 5, and by performing prescribed digital filtering, it is possible to reduce the expected value of the coded error to the minimum remarkably than ever.
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