WIDE-BAND SPEECH SPECTRAL QUANTIZER

A band splitter 3 makes predetermined frequency band splitting and computes each sub-band spectral coefficient for the cut out speech signal. Analyzers 5 and 7 each compute a spectral coefficient vector of each sub-band. Adders 15 and 17 each obtain a result e(i) of subtraction of each sub-band predicted spectral coefficient vector s.sub.-- (i) computed in the band splitter 13 from a spectral coefficient vector s(i). A quantizer 19 quantizes the result e(i) of subtraction for the full band, thus outputting a quantized prediction error vector e.sub.-- (i) from output terminals 21 and 22. A full-band quantized vector E.sub.-- (i) is generated by combining the quantized prediction error vectors c.sub.-- (i) of all the sub-bands. A synthesizer 9 outputs a full-band spectral coefficient vector S.sub.-- (i) by combining the spectral coefficient vectors s(i) of all the sub-bands received from each of the analyzers 5 and 7. An optimum prediction circuit 11 computes a full-band predicted spectral coefficient vector S (i) from the full-band quantized vector E.sub.-- (i) received from the quantizer 19 and the full-band predicted spectral coefficient vector S.sub.-- (i). A band splitter 13 band splits the full-band predicted spectral coefficient vector S (i), and computes each sub-band predicted spectral coefficient vector s.sub.-- (i).