| 摘要 |
A voice decoding apparatus of an adaptive PCM coding system in which an auxiliary controller is provided between a controller and a prediction coefficient holder. The controller 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 extracts, from an ADPCM decoder for decoding a coded signal c, a prediction coefficient g, calculates and stores its average value for each frame and updates the old value with the new one and, at the time of transition from the voice-nonactive duration to the voice-active duration, outputs an immediately stored value h. Even when the input flag e changes from the voice-nonactive duration to the voice-active duration, the auxiliary controller keeps outputting a flag f indicative of the voice-nonactive duration for about five frame periods, thereby preventing degradation of the tone quality of the pseudo-background noise which is generated and decoded by the decoder during the voice-nonactive duration.
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