| 摘要 |
PURPOSE:To obtain satisfactory sound quality irrespective of voice and silent sound by changing the load coefficient of a noise shaping filter and a post noise shaping filter in accordance with the abutment condition of a prediction signal and encoding/decoding a digital input sound signal. CONSTITUTION:A load coefficient selector 66 evaluates the abutment condition of prediction by using digital input sound, short time prediction residual and long time prediction residual signals. Thus, a short time prediction parameter from an LPC parameter/short time prediction parameter converter and a pitch parameter from a decoder are adaptively loaded. They are set in short time prediction unit pole and zero filters 62 and 63, and long time prediction unit pole and zero filters 58 and 59. The result of a prescribed processing is transmitted to a subtractor as the output of the noise shaping filter 19. The transmission function F(z) is given by an expression I, and the filter 19 constitute the long time prediction unit pole and zero filters 58 and 59, and the short time prediction unit pole and zero filters 62 and 63 so that it satisfies the expression I. |
