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Abstract

A voice signal coding apparatus includes: a voice status detector detecting whether an input signal divided at predetermined frame intervals is a voice or a non-voice signal; a linear predictive analyzer outputting a linear predictive parameter associated with the input signal; a voice sound source predicting circuit; a non-voice sound source predicting circuit including a random signal generator; and a switch controller selecting either the voice or non-voice sound source predicting circuit from the detection result of the voice status detector, wherein the random signal gain is set in accordance with a value obtained by suppressing by a predetermined factor the gain obtained when a non-voice input signal is coded by the voice sound predicting circuit. When the input signal is a non-voice signal over a number of successive frames, a switch controller continuously outputs a linear predictive parameter for a previous frame; when a predetermined number of successive non-voice signal frames occurs, the parameter smoothing circuit calculates the weighted sum of the linear predictive parameter of the current frame and a linear predictive parameter used in non-voice frames and outputs a smoothed parameter; and a parameter memory stores the smoothed parameter. The voice status detector includes a threshold value adapting circuit increasing threshold value when the input signal level is greater than the current threshold value and decreasing it when the input signal level is smaller than the current threshold value, wherein the threshold value increasing factor is set to a value greater than a factor by which the threshold value is increased in a normal state.

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First Claim