Voice coding/decoding system including short and long term predictive filters for outputting a predetermined signal as a voice signal in a silence period

摘要

In a voice coding section 1, a digital voice signal coded in a voice coder 10, a linear predictive coefficient used as a filter coefficient in a short-term predictive filter 102, a pitch period and a pitch predictive coefficient used, respectively, as a tap coefficient and a filter coefficient in a long-term predictive filter 103, and voice/no- voice status information of an input voice, are multiplexed in a multiplexer 12. Only when the voice/no-voice status information indicate the voice state is a cell assembled and transmitted. In a voice decoding section 2, the received cell is disassembled to provide multiplexed coded data. The voice signal is decoded by a short-term synthesis filter and a long term synthesis filter. The short term synthesis filter uses a linear predictive coefficient as a filter coefficient that is decoded from multiplexed coded data. The long-term synthesis filter uses a pitch period and a pitch predictive coefficient, respectively, as a tap coefficient and a filter coefficient, where the pitch period and pitch predictive coefficient are decoded from the multiplexed coded data. When the cell has been received, the voice signal is output. When the cell has not been received, a noise signal from a noise generator is output. Thus, a voice coding/decoding system can be provided wherein, even upon a change from a silence period to a speech period, the internal state is smoothly transited avoiding the deterioration in voice quality.