| 摘要 |
A voice coder system capable of coding at low bit rates under 4.8 kb/s with high speech quality. Speech signals are divided into frames and further divided into subframes. A spectral parameter calculator part (200) calculates spectral parameters representing spectral feature of the speech signals in at least one subframe and a spectral parameter quantization part (210) quantizes the spectral parameters of at least one subframe preselected by using a plurality of stages of quantization code books (211) to obtain quantized spectral parameters. A mode classifier part (245) classifies the speech signals in the frame into a plurality of modes by calculating predetermined feature amounts of the speech signals and a weighting part (230) weights perceptual weights to the speech signals by using the spectral parameters obtained in the spectral parameter calculator part to obtain weighted signals. An adaptive code book part (300) obtains pitch parameters representing pitch periods of the speech signals in a predetermined mode by using the mode classification in the mode classifier part, the spectral parameters obtained in the spectral parameter calculator part, the quantized spectral parameters obtained in the spectral parameter quantization part and the weighted signals and a excitation quantization part (350) searches a plurality of stages of excitation code books and a gain code book (355) by using the spectral parameters, the quantized spectral parameters, the weighted signals and the pitch parameters to obtain quantized excitation signals of the speech signals. <IMAGE> |
