Voice signal coding apparatus

A voice signal coding apparatus comprising:

• a voice status detector for detecting whether an input voice signal divided into predetermined frame intervals, is a voice signal or a non-voice signal during each frame interval, a detection that each frame interval is voiced or non-voiced being based on a frame energy of each frame interval;
• a linear predictive analyzer for outputting a linear predictive parameter associated with said input signal;
• a linear predictive coding circuit for generating a driving sound source signal corresponding to a residual linear predictive signal, said linear predictive coding circuit including a voice sound source predicting part for coding a voice signal and a non-voice sound source predicting part for coding a non-voice signal;
• and
• a coding mode selector for selecting either a voice signal coding mode or a non-voice signal coding mode in which said linear predictive coding circuit performs a coding operation, in accordance with a result given by said voice status detector;
• said non-voice sound source predicting part including a random signal generator for generating a random signal representing a sound source signal;
• data coded by said non-voice sound source predicting part including said linear predictive parameter, said random signal, and a gain associated with said random signal;
• and
• said gain associated with said random signal being set in accordance with a gain obtained when said voice sound source predicting part codes a non-voice signal given as the input signal.

A voice signal coding apparatus comprising:

• a voice status detector for detecting whether an input voice signal divided into predetermined frame intervals, is a voice signal or a non-voice signal during each frame interval, a detection that each frame interval is voiced or non-voiced being based on a frame energy of each frame interval;
• a linear predictive analyzer for outputting a linear predictive parameter associated with said input signal;
• a linear predictive coding circuit for generating a driving sound source signal corresponding to a residual linear predictive signal, said linear predictive coding circuit including a voice sound source predicting part for coding a voice signal and a non-voice sound source predicting part for coding a non-voice signal;
• a coding mode selector for selecting either a voice signal coding mode or a non-voice signal coding mode in which said linear predictive coding circuit performs a coding operation, in accordance with a result given by said voice status detector;
• a controller for controlling the linear predictive parameter such that when the detection result by said voice status detector indicates that the input signal is a non-voice signal over a predetermined number of successive frames, the linear predictive parameter employed for a previous frame is continuously employed as the linear predictive parameter for the input signal;
• a smoothing circuit for smoothing the linear predictive parameter for use in non-voice frames in such a manner that when a number of successive frames regarded as including a non-voice signal exceeds said predetermined number, smoothing is performed between a previously-prepared linear predictive parameter for use in non-voice frames and a linear predictive parameter associated with the current frame, and the resultant smoothed linear predictive parameter is output.

A voice signal coding apparatus comprising:

• a voice status detector for detecting whether an input voice signal divided into predetermined frame intervals, is a voice signal or a non-voice signal during each frame interval, a detection that each frame interval is voiced or non-voiced being based on a frame energy of each frame interval;
• a linear predictive analyzer for outputting a linear predictive parameter associated with said input signal;
• a linear predictive coding circuit for generating a driving sound source signal corresponding to a residual linear predictive signal, said linear predictive coding circuit including a voice sound source predicting part for coding a voice signal and a non-voice sound source predicting part for coding a non-voice signal;
• a coding mode selector for selecting either a voice signal coding mode or a non-voice signal coding mode in which said linear predictive coding circuit performs a coding operation, in accordance with a result given by said voice status detector;
• said voice signal status detector comprising:
• a level measuring circuit for measuring a level of an input signal divided at predetermined frame intervals;
• a comparator for comparing the level of said input signal measured by said level measuring circuit with a threshold value provided as a criterion for determining whether said input signal is a voice signal or a non-voice signal and then outputting the comparison result;
• and
• a threshold value adapting circuit by which said threshold value is increased by a predetermined factor when said comparator has determined that the level of said input signal is greater than a current threshold value, while said threshold value is decreased when said comparator has determined that the level of said input signal is smaller than the current threshold value, wherein said predetermined factor by which said threshold value is increased is set in accordance with a difference between the current threshold value and a minimum level of the input signal during a predetermined period of past time.

A method for coding voice signals comprising the steps of:

• receiving an input voice signal comprised of voice and non-voice signal components;
• dividing the receiving input signal into predetermined frames of a given interval;
• examining each frame to determine if it is a voice or non-voice signal;
• and
• respectively coding one of a voice signal and a non-voice signal for each frame responsive to identification of said frame as having a voice or non-voice signal;
• said non-voice signal including a random signal which is employed as a sound source signal;
• and
• selecting a predicted sound source signal from probability code vectors stored in a probability code book, determining an energy in the predicted sound source signal selected and modifying the random signal by adjusting a gain of the random signal until an energy of the generated random signal is substantially equal to the energy of the predicted sound source signal.

A method for coding voice signals comprising the steps of:

• receiving an input voice signal comprised of voice and non-voice signal components;
• dividing the receiving input signal into predetermined frames of a given interval;
• examining each frame to determine if it is a voice or non-voice signal;
• respectively coding one ofa voice signal and a non-voice signal for each frame responsive to identification of said frame as having a voice or non-voice signal;
• said non-voice signal including a random signal which is employed as a sound source signal;
• and
• selecting a predicted sound source signal from probability code vectors stored in a probability code book, determining an energy in the predicted sound source signal selected and modifying the random signal by adjusting a gain of the random signal until an energy of the generated random signal is substantially equal to the energy ofthe predicted sound source signal;
• and
• generating a linear predictive parameter representing a spectrum characteristic of the input signal;
• modifying the coded non-voice signal by said parameter subtracting the modified coded non-voice signal from a sub-frame of the input signal to generate an error vector;
• weighting the error vector according to audibility characteristics;
• and
• calculating a mean square ofthe error vector which is employed to select an optimum code stored in the probability code book.

A voice signal coding apparatus comprising:

• a voice status detector for detecting whether an input signal comprised of voice and non-voice components and divided at predetermined frame intervals, is a voice signal or a non-voice signal;
• a linear predictive analyzer outputting a linear predictive parameter associated with said input signal;
• a linear predictive coder for generating a driving sound source signal corresponding to a residual linear predictive signal, said linear predictive coder including a voice sound source predicting part for coding a voice signal and a non-voice sound source predicting part for coding a non-voice signal;
• a coding mode selector for selecting either a voice signal coding mode or a non-voice signal coding mode in which said linear predictive coder performs a coding operation, in accordance with a result given by said voice status detector;
• said non-voice sound source predicting part including a random signal generator for generating a random signal representing a sound source signal;
• a circuit for adjusting a gain of the random signal employing an output from the voice sound source predicting part;
• a device employing the linear predictive parameter to modify the input signal;
• a subtractor subtracting the modified input signal from the original input signal;
• and
• a circuit for evaluating the result of the subtracting circuit to modify a coded signal from one of said voice and non-voice sound signal predicting parts.

A voice signal coding apparatus comprising:

• a voice status detector for detecting whether an input voice signal divided into predetermined frame intervals, is a voice signal or a non-voice signal during each frame interval, a detection that each frame interval is voiced or non-voiced being based on a frame energy of each frame interval;
• a linear predictive analyzer for outputting a linear predictive parameter associated with said input signal;
• a linear predictive coding circuit for generating a driving sound source signal corresponding to a residual linear predictive signal, said linear predictive coding circuit including a voice sound source predicting part for coding a voice signal and a non-voice sound source predicting part for coding a non-voice signal;
• a coding mode selector for selecting either a voice signal coding mode or a non-voice signal coding mode in which said linear predictive coding circuit performs a coding operation, in accordance with a result given by said voice status detector.
• said voice signal status detector comprising:
• a first frame analyzer for determining an energy of an initial frame;
• a threshold decision circuit for determining a threshold value based on an output of the first frame analyzer;
• a second frame analyzer for detecting energy of at least one frame subsequent to the initial frame;
• a third circuit for subtracting the initial frame energy from the output of said second frame analyzer;
• and
• a detector for comparing a difference value outputted by the the third circuit with the threshhold value generated by said threshold decision circuit to determine whether an examined frame is voice or non-voice, said determination being available for a frame immediately following the initial frame.

A method for coding voice signals comprising the steps of:

• (a) receiving an input voice signal comprised of voice and non-voice signal components;
• (b) dividing the receiving input signal into predetermined frames of a given interval;
• (c) examining each frame to determine if it is a voice or non-voice signal;
• (d) respectively coding one of a voice signal and a non-voice signal for each frame responsive to identification of said frame as having a voice or non-voice signal;
• said non-voice signal including a random signal which is employed as a sound source signal;
• and
• (e) selecting a predicted sound source signal from probability code vectors stored in a probability code book, determining an energy in the predicted sound source signal selected and modifying the random signal by adjusting a gain of the random signal until an energy of the generated random signal is substantially equal to the energy ofthe predicted sound source signal;
• (f) step (c) further comprising measuring a level of an input signal of each frame;
• (g) comparing the level of said input signal at step (f) with a threshold value provided as a criterion for determining whether said input signal is a voice signal or a non-voice signal and then outputting the comparison result;
• and
• (h) increasing said threshold value by a predetermined factor when the comparing step (g) determines that the level of said input signal is greater than a current threshold value, and decreasing said threshold value when said comparing step (g) determines that the level of said input signal is smaller than the current threshold value, wherein said predetermined factor by which said threshold value is changed is set in accordance with a difference between the current threshold value and a minimum level of the input signal during a predetermined period of past time.

A voice signal coding apparatus comprising:

• a voice status detector for detecting whether an input signal divided at predetermined frame intervals is a voice signal or a non-voice signal;
• a linear predictive analyzer outputting a linear predictive parameter associated with said input signal;
• a linear predictive coder for generating a driving sound source signal corresponding to a residual linear predictive signal, said linear predictive coder including a voice sound source predicting part for coding a voice signal and a non-voice sound source predicting part for coding a non-voice signal;
• a coding mode selector for selecting either a voice signal coding mode or a non-voice signal coding mode in which said linear predictive coder performs a coding operation, in accordance with a result given by said voice status detector;
• said non-voice sound source predicting part including a random signal generator for generating a random signal representing a sound source signal;
• a circuit for adjusting a gain of the random signal employing an output from the voice sound source predicting part;
• a device employing the linear predictive parameter to modify the input signal;
• a subtractor subtracting the modified input signal from the original input signal;
• and
• a circuit for evaluating the result of the subtracting circuit to modify a coded signal from one of said voice and non-voice sound signal predicting parts;
• and
• a voice signal status detector comprising:
• a level measuring circuit for measuring a level of an input signal divided at predetermined frame intervals;
• a comparator for comparing the level of said input signal measured by said level measuring circuit with a threshold value provided as a criterion for determining whether said input signal is a voice signal or a non-voice signal and then outputting the comparison result;
• and
• a threshold value adapting circuit by which said threshold value is increased by a predetermined factor when said comparator has determined that the level of said input signal is greater than a current threshold value, while said threshold value is decreased when said comparator has determined that the level of said input signal is smaller than the current threshold value, wherein said predetermined factor by which said threshold value is increased is set in accordance with a difference between the current threshold value and a minimum level of the input signal during a predetermined period of past time.