| 摘要 |
A speech coder capable of achieving an excellent sound quality even at a low bit rate. A mode judging circuit 800 of the speech coder judges a mode by the use of a feature quantity of an input speech signal for each subframe. In case of a predetermined mode, an excitation quantization circuit 350 searches combinations of every code vectors stored in codebooks 351 and 352 for simultaneously quantizing amplitudes or polarities of a plurality of pulses and each of a plurality of shift amounts for temporally shifting predetermined pulse positions, and selects a combination of the code vector and the shift amount which minimizes distortion from an input speech. A gain quantization circuit 365 quantizes a gain by the use of a gain codebook 380.
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