| 摘要 |
TITLE OF THE INVENTION A Speech Signal Coding/Decoding System input speech signal is encoded by an adaptive quantizer (16) which quantizes the predicted residual signal between the digital input speech signal, and prediction signals provided by predictors (6,10) and a shaped quantization noise provided by a noise shaping filter (19). An inverse quantizer (18) which the encoded speech signal is supplied to, is provided for noise shaping and local decoding. A noise shaping filter (19) around the adaptive quantizer makes the spectrum of the quantization noise similar to that of the original digital input speech signal by using the shaping factors. The shaping factors (rn1, rns) set to the noise shaping filter (19) are adaptively switched to weight it depending upon the prediction gain (ex. ratio of input speech signal to predicted residual signal or the prediction coefficients). In a decoding side there are an inverse quantizer (36), predictors (42,43), and a post noise shaping filter (44). The shaping factors set to the post noise shaping filter are similary switched to weight it depending upon the prediction gain. |
