| 摘要 |
PURPOSE:To obtain a DPCM having excellent coding characteristics to voice and other signals, by attaining encoding to a signal having very different characteristics while preserving properties strong in transmission line bit error. CONSTITUTION:A subtractor 21 subtracts a time-unchanged forecasting signal suitable for average characteristic signal of a voice/data MODEM signal from an input signal xj. The result is added with a quantized residual signal changing timewise the characteristic from an adaptive filter 61 and a residual signals ej is obtained from a subtractor 22. This ej is encoded by a quantizer 3 by using the quantized width and outputted from a terminal 7. On the other hand, a local decoding signal zj is subtracted by subtractors 82, 81 with output signal of time- unchanged forecasting filters 63, 64, and the absolute values are compared by a comparator 85. A coefficient alpha multiplied with the time unchanged forecasting of a low-pass filter 86 is changed in the range of 0-1 from the result of comparison; nearly alpha=1 at the voice input and nearly alpha=0 at the data MODEM signal input. |
