| 摘要 |
PROBLEM TO BE SOLVED: To reduce a wave distortion caused by selecting a fixed code book when an input widely changes in aural frequency components in encoding used by changing over an adaptive code book and a fixed code book to/from each other for a selection such as PSI-CELP(pitch synchronous innovation-code excited linear prediction). SOLUTION: An output from an adaptive code book 21 or an output from a fixed code book 22 is selected by a selection switch 26 and is added to outputs from noise code books 23, 24, for being sent to a linear prediction synthesis filter 16. A switch control circuit 19 controlling the selection switch 26 discriminates a voiced sound according to a prediction gain, the ratio of a linear prediction residual energy to an initial signal energy from a linear prediction analyzing circuit 14, when this prediction gain is smaller than a prescribed threshold, and controls the selection switch 26 to forcibly select the output from the adaptive code book 21. |
