Communication system capable of improving a speech quality by effectively calculating excitation multipulses

Claim 2

An encoder device supplied with a sequence of digital speech signals at every frame to produce a sequence of output signals, each frame having N samples per a single frame where N represents an integer, said digital speech signals being classified into a voiced sound and an unvoiced sound, said encoder device comprising parameter calculation means responsive to said digital speech signals for calculating first and second parameters which specify a spectrum envelope and a pitch of the digital speech signals at every frame to produce first and second parameter signals representative of said spectrum envelope and said pitch, respectively, pulse calculation means coupled to said parameter calculation means for calculating a set of calculation result signals representative of said digital speech signals, and output signal producing means for producing said set of the calculation result signals as said output signal sequence, wherein the improvement comprises: judging means operable in cooperation with said parameter calculation means for judging whether said digital speech signals are classified into said voiced sound or said unvoiced sound at every frame to produce a judged signal representative of a result of judging said digital speech signals; said pulse calculation means comprising: processing means supplied with said digital speech signals, said first and said second parameter signals, and said judged signal for processing said digital speech signals in accordance with said judged signal to selectively produce a first set of primary sound source signals and a second set of secondary sound source signals different from said first set of the primary sound source signals, said first set of the primary sound source signals being representative of locations and amplitudes of a first set of excitation multipulses calculated at every frame, said second set of the secondary sound source signals being representative of the amplitudes of a second set of excitation multipulses each of which is located at intervals of a preselected number of the samples; and means for supplying a combination of said first and said second parameter signals, said judged signal, and said primary and said secondary sound source signals to said output signal producing means.

Claim 3

An encoder device as claimed in claim 1, wherein said processing means produces said first set of the primary sound source signals when said judged signal is representative of said voiced sound and, otherwise, produces said second set of the secondary sound source signals.

Claim 4

An encoder device as claimed in claim 1, wherein said judging means compares said pitch with a predetermined level to judge whether said speech signal is classified into the voiced sound or the unvoiced sound.

Claim 5

An encoder device as claimed in claim 1, each frame being divided into a predetermined number of subframes each of which has a predetermined duration, wherein said processing means calculates, in response to said judged signal representative of said unvoiced sound, amplitudes of a plurality of excitation multipulses and an initial phase of a first excitation multipulse located at a head of said plurality of the excitation multipulses in each of said subframes by the use of said first parameters, said processing means producing a sequence of said initial phases of said subframes and a sequence of said plurality of excitation multipulses of said subframes as said second set of secondary sound source signals.

Claim 6

An encoder device as claimed in claim 4, wherein said processing means comprises: impulse response calculating means responsive to said first and said second parameter signals and said judged signal for calculating a primary impulse response by the use of said first and said second parameters when said judged signal represents said voiced sound and for calculating a secondary impulse response by the use of said first parameter when said judged signal represents said unvoiced sound to selectively produce a primary impulse response signal representative of said primary impulse response and a secondary impulse response signal representative of said secondary impulse response; cross-correlation calculating means responsive to said digital speech signals, said primary and said secondary impulse response signals, and said judged signal for calculating primary cross-correlation coefficients by the use of said primary impulse response when said judged signal represents said voiced sound and for calculating secondary cross-correlation coefficients by the use of said secondary impulse response when said judged signal represents said unvoiced sound to selectively produce a primary cross-correlation signal representative of said primary cross-correlation coefficients and a secondary cross-correlation signal representative of said secondary cross-correlation coefficients; autocorrelation calculating means responsive to said primary and said secondary impulse response signal for calculating primary autocorrelation coefficients by the use of said primary impulse response and for calculating secondary autocorrelation coefficients by the use of said secondary impulse response to selectively produce a primary autocorrelation signal representative of said primary autocorrelation coefficients and a secondary autocorrelation signal representative of said secondary autocorrelation coefficients; and a pulse calculator responsive to said judged signal, said primary and said secondary cross-correlation signals, and said primary and said secondary autocorrelation signals for calculating the locations and the amplitudes of said first set of the excitation multipulses by the use of said primary cross-correlation and autocorrelation coefficients at every frame when said judged signal represents said voiced sound and for calculating the amplitudes of said plurality of excitation multipulses and the initial phase of said first excitation multipulse by the use of said secondary cross-correlation and autocorrelation coefficients in each of said subframes when said judged signal represents said unvoiced sound to selectively produce the locations and the amplitudes of said first set of the excitation multipulses as said primary sound source signals and said sequence of the initial phases of said subframes and said sequence of the plurality of excitation multipulses of said subframes as said second set of secondary sound source signals.

Claim 7

An encoder device as claimed in claim 1, wherein said processing means calculates, in response to said judged signal representative of said unvoiced sound, amplitudes of a plurality of excitation multipulses and an initial phase of a first excitation multipulse located at a head of said plurality of excitation multipulses in each of subframes, which result from dividing every frames and each of which is shorter than said frame, by the use of cross-correlation coefficients specified by said first parameters and said second parameters, said processing means producing a sequence of said initial phases of said subframes and a sequence of said excitation multipulses of said subframes as said second set of secondary sound source signals.

Claim 8

An encoder device as claimed in claim 6, said processing means comprises; impulse response calculating means responsive to said first and said second parameter signals for calculating an impulse response by the use of said first and said second parameters to produce an impulse response signal representative of said impulse response; cross-correlation calculating means responsive to said digital speech signals, and said impulse response signal for calculating cross-correlation coefficients by the use of said impulse response to produce a cross-correlation signal representative of said cross-correlation coefficients; autocorrelation calculating means responsive to said impulse response signal for calculating autocorrelation coefficients by the use of said impulse response to produce an autocorrelation signal representative of said autocorrelation coefficients; and a pulse calculator responsive to said judged signal, said cross-correlation signals, and said autocorrelation signals for calculating the locations and the amplitudes of said first set of the excitation multipulses by the use of said cross-correlation and autocorrelation coefficients at every frame when said judged signal represents said voiced sound and for calculating the amplitudes of said plurality of excitation multipulses and the initial phase of said first excitation multipulse by the use of said cross-correlation and autocorrelation coefficients in each of said subframes when said judged signal represents said unvoiced sound to selectively produce the locations and the amplitudes of said first set of the excitation multipulses as said primary sound source signals and said sequence of the initial phases of said subframes and said sequence of the plurality of excitation multipulses of said subframes as said second set of secondary sound source signals.

Claim 9

A decoder device communicable with the encoder device claimed in claim 1 to produce a sequence of synthesized speech signals, said decoder device being supplied with said output signal sequence as a sequence of reception signals which carries said first set of the primary sound source signals, said second set of the secondary sound source signals, said first and said second parameter signals, and said judged signal, said decoder device comprising: demultiplexing means supplied with said reception signal sequence for demultiplexing said reception signal sequence into the first set of primary sound source signals, the second set of secondary sound source signals, the first and the second parameter signals, and the judged signals as a first set of primary sound source codes, a second set of secondary sound source codes, first and second parameter codes, and judged codes, respectively; decoding means coupled to said demultiplexing means for decoding said first set of the primary sound source codes into a first set of decoded primary sound source signals when said judged codes are representative of said voiced sound and for decoding said second set of secondary sound source codes into a second set of decoded secondary sound source signals when said judged codes are representative of said unvoiced sound; parameter decoding means coupled to said demultiplexing means for decoding said first and said second parameter codes into first and second decoded parameters, respectively; pulse generating means coupled to said demultiplexing means, said decoding means, and said parameter decoding means for generating a first set of driving sound source signals by the use of said decoded second parameters when said judged signal is representative of said voiced sound and for generating a second set of driving source signals by the use of said decoded second parameters when said judged signal is representative of said unvoiced sound; and means coupled to said pulse generating means and said parameter decoding means for synthesizing said first set and said second set of the driving sound source signals into said synthesized speech signals by the use of said first decoded parameters.