PURPOSE: To reduce an arithmetic quantity and to enable efficient tree encoding by making a tree search while tracing optimum code sequence candidates in the generation order, and regarding a code sequence which has small quantization distortion as the best code sequence candidate when the code sequence is obtained.
CONSTITUTION: Signals which are obtained by converting speech signals inputted from an input terminal 1 into digital values by an A/D converter 2 are stored on a buffer 3, and an encoder 4 consists of a tree encoder 41 and a quantizer 42 and finds the code sequence having the smallest quantization distortion by encoding. Then while the code sequences of the best code sequence candidates are traced in the reverse generation order, the code sequence having small quantization distortion is searched for and when a code sequence which has smaller quantization distortion than the best code sequence candidate is obtained, the code sequence is regarded newly as the optimum code sequence candidate. When the code sequence having smaller quantization distortion is not obtained, on the other hand, the best code sequence candidate is specified as the best code sequence. Consequently, the best code sequence is searched for by a tree encoding system with the small storage capacity of parameters and a small arithmetic quantity.
MORIO TOMOKAZU
FUJIMOTO KOJI
