| 摘要 |
A decoder compares a spectral envelope value y8 on a frequency axis with a predetermined threshold f9 to identify a voiced region and an unvoiced region. An excitation signal is produced by using excitations suitable for respective frequency regions. An encoder applies the nonuniform quantization to the period of the aperiodic pitch in accordance with its frequency of occurrence. The result of the nonuniform quantization is transmitted together with the quantization result of the unvoiced state and the periodic pitch as one code. A decoder obtains spectral envelope amplitude l8' from the spectral envelope information, and identifies a frequency band e10' where the spectral envelope amplitude value is maximized in each of respective bands divided on the frequency axis. A mixing ratio g8', which is used in mixing a pitch pulse generated in response to the pitch period information and white noise, is determined based on the identified frequency band and voiced/unvoiced discriminating information. A mixing signal of each frequency band is produced in accordance with the mixing ratio. Then, the mixing signals of respective frequency bands are summed up to produce a mixed excitation signal x8'.
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