| 摘要 |
To prevent a pseudo-background noise for a voice-nonactive duration at the receiving side from having unnatural tone quality in a receiving side, a voice decoding apparatus of the adaptive PCM coding system comprises an auxiliary controller (6) provided between a controller (5) and a prediction coefficient holder (7). The controller (5) receives a voice activity detection flag (b) separated from a received demodulated signal (a) and, at the time of transition from the voice-active duration to the voice-nonactive duration and vice versa, outputs a reset signal (d) and a signal (e) indicating whether the voice activity detection flag is voice-active or voice-nonactive. The prediction coefficient holder (7) extracts, from an ADPCM decoder (4) for decoding a coded signal (c), a prediction coefficient (g), calculates and stores its average value for each frame and update the old value with the new one and, at the time of transition from the voice-active duration to the voice non-active duration, outputs an immediately stored value (h). Even when the input flag (e) changes from the voice-non active duration to the voice-active duration, the auxiliary controller (6) keeps on outputting a flag (f) indicative of the voice-nonactive duration for about five frame periods, thereby preventing the degradation of the tone quality of the pseudo-background noise which is generated and decoded by a decoder (4) during the voice-nonactive duration. <IMAGE>
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