METHOD FOR SELECTING ADAPTIVE CODE BOOK FOR VOICE CODEC

摘要

PROBLEM TO BE SOLVED: To provide a method of selecting an adaptive code book for a voice Codec in order to obtain a digital type portable telephone low in power consumption and excellent in talking tone quality. SOLUTION: In a method of selecting an adaptive code book for a voice Codec frame-processed with switching output between a fixed code book and an adaptive code book selected by pitch-analyzing a voice signal and the output of a noise code book of multichannel structure, as driving source, a normal pitch prospect group 38 and a reduced pitch prospect group 39 less in the number of prospects than the normal pitch prospect group 38 are outputted at the time of pitch-analyzing the voice signal. The reduced pitch prospect group 39 is selected when the voice Codec processing of a preceding frame exceeds frame time, while the normal pitch prospect group 38 is selected at the time of not exceeding the frame time, and an adaptive code book 32 is selected by the pitch prospect group 38 or 39.