Multipulse processing with freedom given to multipulse positions of a speech signal

• US 5,696,874 A
• Filed: 12/06/1994
• Issued: 12/09/1997
• Est. Priority Date: 12/10/1993
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Taguchi, Tetsu
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): Wieland, Susan
• Application Number:
  US08/354,105
• Time in Patent Office: 1,099 Days
• Field of Search: 381/30, 381/31, 381/36, 381/38, 395/2.28, 395/2.31, 395/2.74
• US Class Current: 704/219
• CPC Class Codes: G10L 19/10 the excitation function being a multipulse excitation

Abstract

In a multipulse processing device for achieving a high encoding efficiency without using a high sampling frequency for an input signal and with a great degree of freedom given to positions of multipulses, an input speech signal is subjected by an LPC analyzer/processor 3 to LPC analysis of each analysis frame for extraction of LPC coefficients after sampled by an A/D converter 2. Multipulses are retrieved as a result of decision by a multipulse analyzer 20 with a degree of freedom given relative to sampling points of a sampled speech signal supplied through an auditorily weighting filter 4. Encoded by an encoder 41 and together with k parameters used as an example of the LPC coefficients, retrieved multipulses are multiplexed by a multiplexer 42 for delivery to a synthesis side. A multipulse waveform synthesizer 45 synthesizes a waveform by using decoded multipulse data and the LPC coefficients.

Claims

1. A multipulse processing method of multipulse encoding an input speech signal on an analyzing side into an encoded speech signal for multipulse synthesis of said encoded speech signal on a synthesizing side into a synthesized speech signal equivalent to said input speech signal, said multipulse processing method comprising on said analyzing side the steps of sampling said input speech signal into a sampled speech signal at a predetermined sampling frequency defining successive analysis frames, linear predictive coding (LPC) analyzing said sampled speech signal of each analysis frame to extract LPC coefficients and to produce original spectrum envelope information of said input speech signal based on said LPC coefficients, multipulse analyzing said LPC coefficients into a sequence of original multipulses having appearance time instants at which said original multipulses appear and multipulse amplitudes in correspondence in each analysis frame to features of excitation source information representative of speech information of said input speech signal in combination with said spectrum envelope information, and encoding said sequence of original multipulses and said spectrum envelope information into an encoded sequence of original multipulses and encoded spectrum envelope information for use in combination as said encoded speech signal, wherein said multipulse analyzing step comprises the step of giving a degree of freedom to said appearance time instants relative to sampling instants of said sampled speech signal, so that said appearance time instants are modified without increasing said predetermined sampling frequency, to modify said original multipulses into modified multipulses to make said encoded sequence comprise said modified multipulses in place of said original multipulses.

2. A multipulse processing method as claimed in claim 1, said multipulse analyzing step comprising the steps of calculating an impulse response in response to said LPC coefficients, calculating cross-correlation coefficients between said sampled speech signal and said impulse response, and calculating autocorrelation coefficients of said impulse response, wherein said freedom giving step comprises the steps of:

interpolating said autocorrelation coefficients by a greatest absolute value of maxima and minima of said cross-correlation coefficients into interpolated autocorrelation coefficients;

correcting responsive to said interpolated autocorrelation coefficients said cross-correlation coefficients into corrected cross-correlation coefficients; and

repeating said interpolating step and said correcting step to repeatedly use the greatest absolute value of maxima and minima of said corrected cross-correlation coefficients a predetermined number of times and to use time positions and extremum amplitudes of maxima and minima of said corrected cross-correlation coefficients as the appearance time instants given said degree of freedom and as said multipulse amplitudes.

3. A multipulse processing method as claimed in claim 2, wherein said interpolating step comprises the steps of:

detecting, in each instance of said predetermined number of times, an extremum of said corrected cross-correlation coefficients by interpolation in at least three consecutive samples comprising one of the maxima and the minima of said corrected cross-correlation coefficients and two samples preceding and following one sampling period of said sampling frequency said one of maxima and minima of said corrected cross-correlation coefficients; and

detecting, as said greatest absolute value, a greatest amplitude of the extrema detected during said predetermined number of times.

4. A multipulse processing method as claimed in claim 1, said multipulse analyzing step comprising the step of calculating responsive to said LPC coefficients an impulse response, wherein:

said multipulse analyzing step comprises the steps of;

upsampling said sampled speech signal and said impulse response into an upsampled speech signal and an upsampled impulse response at an analysis reference frequency higher than said sampling frequency;

calculating upsampled cross-correlation coefficient between said upsampled speech signal and said upsampled impulse response; and

calculating upsampled autocorrelation coefficients of said upsampled impulse response; and

that;

said freedom giving step comprises the step of detecting in response to said upsampled cross-correlation coefficients and said upsampled autocorrelation coefficients said modified multipulses with the appearance time instants of said original multipulses given said degree of freedom and with said multipulse amplitudes.

5. A multipulse processing method as claimed in claim 1, said multipulse analyzing step comprising the steps of calculating in response to said LPC coefficients an impulse response, calculating cross-correlation coefficients between said sampled speech signal and said impulse response, and calculating autocorrelation coefficients of said impulse response, wherein:

said multipulse analyzing step further comprises the steps of;

multiphase processing a sequence of said cross-correlation coefficients into a plurality of pulse sequences having said sampling frequency in common and different phases; and

detecting a plurality of multipulse sequences in response to said autocorrelation coefficients from said pulse sequences, respectively;

said freedom giving step producing in response to said sampled speech signal and said pulse sequences said modified multipulses with the appearance time instants of said original multipulses given said degree of freedom and with said multipulse amplitudes.

6. A multipulse processing method as claimed in claim 5, wherein said freedom giving step comprises the steps of:

locally synthesizing said pulse sequences into a plurality of sampled trains of samples in concurrency with said sampled speech signal; and

selecting, as said modified multipulses, the samples of one of said sampled trains that has a signal-to-noise (S/N) ratio with said sampled speech signal used as a signal and with differences between said sampled speech signal and said sampled trains used as noise.

7. A multipulse processing method as claimed in claim 1, wherein said freedom giving step reduces said degree of freedom by mapping the appearance time instants given said degree of freedom onto a time axis of sampling instants defined by said sampling frequency.

8. A multipulse processing method as claimed in claim 1, further comprising on said synthesizing side the step of decoding the encoded sequence and the encoded spectrum envelope information of said encoded speech signal into a decoded sequence of modified multipulses and decoded spectrum envelope information, wherein said multipulse processing method comprises on said synthesizing side the step of multipulse waveform synthesizing said decoded sequence of modified multipulses and said decoded spectrum envelope information into said synthesized speech signal, said multipulse waveform synthesizing step comprising the steps of:

LPC synthesizing in response to said decoded spectrum envelope information said decoded sequence of modified multipulses into a plurality of primary synthesized outputs having said sampling frequency in common and phases different depending on differences between said modified and said original multipulses;

upsampling said primary synthesized outputs by a synthesis reference clock signal of a higher frequency than said sampling frequency into secondary synthesized outputs having said higher frequency in common and said phases;

summing up said secondary synthesized outputs into a sum output of said higher frequency and a predetermined one of said phases; and

D/A converting said sum output into said synthesized speech signal.

9. A multipulse processing method as claimed in claim 1, further comprising on said synthesizing side the step of decoding the encoded sequence and the encoded spectrum envelope information of said encoded speech signal into a decoded sequence of modified multipulses and decoded spectrum envelope information, said multipulse processing method being characterized by comprising on said synthesizing side the step of multipulse waveform synthesizing said decoded sequence of modified multipulses and said decoded spectrum envelope information into said synthesized speech signal, said multipulse waveform synthesizing step comprising the steps of:

LPC synthesizing in response to said decoded spectrum envelope information said decoded sequence of modified multipulses into a plurality of primary synthesized waveform trains having said sampling frequency in common and phases dependent on differences between said modified and said original multipulses;

up/down sampling said primary synthesized waveform trains, such that said primary synthesized waveform trains are up sampled in response to a synthesis reference clock signal of a higher frequency than said sampling frequency to produce upsampled primary synthesized waveform trains which are down sampled in response to timing pulse sequences having said sampling frequency in common and said phases, to generate secondary synthesized waveform trains having said sampling frequency in common and one of said phases that is specified by a predetermined one of said timing pulse sequences;

summing up said secondary synthesized waveform trains into a sum waveform sequence; and

digital-to-analog (D/A) converting said sum sequence into said synthesized speech signal.

10. A multipulse processing method as claimed in claim 1, further comprising on said synthesizing side the step of decoding the encoded sequence and the encoded spectrum envelope information of said encoded speech signal into a decoded sequence of modified multipulses and decoded spectrum envelope information, wherein said multipulse processing method comprises on said synthesizing side the step of multipulse waveform synthesizing said decoded sequence of modified multipulses and said decoded spectrum envelope information into said synthesized speech signal, said multipulse waveform synthesizing step comprising the steps of:

generating trains of discrete pulses by correlation processing of said decoded spectrum envelope information, the discrete pulses of each of said trains having pulse positions corresponding to said modified pulses, the pulse positions in said trains being different in correspondence to differences between said modified and said original multipulses;

LPC synthesizing in response to said decoded spectrum envelope information and said trains of discrete pulses said decoded sequence of modified multipulses into a synthesized waveform sequence; and

digital-to-analog (D/A) converting said synthesized waveform sequence into said synthesized speech signal.

11. A multipulse encoding device comprising sampling means for sampling an input speech signal into a sampled speech signal at a predetermined sampling frequency defining successive analysis frames, linear predictive coding (LPC) analyzing means for LPC analyzing said sampled speech signal of each analysis frame to extract LPC coefficients and to produce spectrum envelope information of said input speech signal based on said LPC coefficients, multipulse analyzing means for multipulse analyzing said LPC coefficients into a multipulse sequence of multipulses having appearance time instants at which said original multipulses appear and multipulse amplitudes in correspondence in each analysis frame to features of excitation source information representative of speech information of said input speech signal in combination with said spectrum envelope information, and encoding means for encoding said excitation source information into an encoded sequence to produce said encoded signal and said spectrum envelope information as an encoded speech signal, wherein said multipulse analyzing means comprises freedom giving means for giving a degree of freedom to said appearance time instants relative to sampling time instants of said sampled speech signal, so that said appearance time instants are modified without increasing said predetermined sampling frequency, to make said encoding means use the excitation source information in which the appearance time instants of said multipulses are given said degree of freedom.

12. A multipulse encoding device as claimed in claim 11, said multipulse analyzing means comprising an impulse response calculator responsive to said LPC coefficients for calculating an impulse response, cross-correlation calculating means for calculating cross-correlation coefficients between said sampled speech signal and said impulse response, and an autocorrelation calculator for calculating autocorrelation coefficients of said impulse response, wherein said freedom giving means comprises a loop comprising:

interpolating means for interpolating said autocorrelation coefficients by a greatest absolute value of maxima and minima of said cross-correlation coefficients into interpolated autocorrelation coefficients; and

correcting means responsive to said interpolated autocorrelation coefficients for correcting said cross-correlation coefficients into corrected cross-correlation coefficients to repeatedly use the greatest absolute value of maxima and minima of said corrected cross-correlation coefficients a predetermined number of times and to use time positions and extremum amplitudes of the maxima and the minima of said corrected cross-correlation coefficients as the appearance time instants given said degree of freedom and as said multipulse amplitudes.

13. A multipulse encoding device as claimed in claim 12, wherein said interpolating means comprises:

extremum detecting means connected to said correcting means for detecting, in each instance of said predetermined number of times, an extremum of said corrected cross-correlation coefficients by interpolation in at least three consecutive samples comprising one of the maxima and the minima of said corrected cross-correlation coefficients and two samples preceding and following one sampling period of said sampling frequency said one of maxima and minima of corrected cross-correlation coefficients; and

amplitude detecting means for detecting, as said greatest absolute value, a greatest absolute amplitude of the extrema detected during said predetermined number of times.

14. A multipulse encoding device as claimed in claim 11, said multipulse analyzing means comprising an impulse response calculator responsive to said LPC coefficients for calculating an impulse response, wherein:

said multipulse analyzing means comprises;

upsampling means for upsampling said sampled speech signal and said impulse response into an upsampled speech signal and an upsampled impulse response at an analysis reference frequency higher than said sampling frequency;

an upsampled cross-correlation calculator for calculating upsampled cross-correlation coefficients between said upsampled impulse speech signal and said upsampled response; and

an upsampled impulse autocorrelation calculator for calculating upsampled autocorrelation coefficients of said upsampled response;

said freedom giving means detecting in response to said upsampled cross-correlation coefficients and said upsampled autocorrelation coefficients the multipulses having the appearance time instants given said degree of freedom and said multipulse amplitudes.

15. A multipulse encoding device as claimed in claim 11, said multipulse analyzing means comprising an impulse response calculator responsive to said LPC coefficients for calculating an impulse response, cross-correlation calculating means for calculating cross-correlation coefficients between said sampled speech signal and said impulse response, and an autocorrelation calculator for calculating autocorrelation coefficients of said impulse response, wherein:

said multipulse analyzing means further comprises;

a multiphase processor for multiphase processing a sequence of said cross-correlation coefficients into a plurality of pulse sequences having said sampling frequency in common and different phases; and

a multipulse detector for detecting a plurality of multipulse sequences in response to said autocorrelation coefficients from said pulse sequences, respectively;

said freedom giving means producing in response to said sampled speech signal and said pulse sequences the multipulses with the appearance time instants given said degree of freedom and with said multipulse amplitudes.

16. A multipulse encoding device as claimed in claim 15, wherein said freedom giving means comprises:

local synthesis filters for synthesizing said pulse sequences into a plurality of synthesized outputs;

local sampling means for sampling said synthesized outputs into a plurality of sampled trains of samples sampled in concurrency with said sampled speech signal; and

selecting means for selecting, as the multipulses with the appearance time instants given said degree of freedom and with said multipulse amplitudes, the samples of one of said sampled trains that has a best S/N ratio with said sampled speech signal used as a signal and with differences between said sampled speech signal and said sampled trains used as noise.

17. A multipulse encoding device as claimed in claim 16, wherein:

said selecting means produces an indicatiohn signal indicative of the samples of said one of sampled trains;

said encoding means using said sampled trains and said indication signal collectively as the excitation source information in which the appearance time instants are given said degree of freedom.

18. A multipulse encoding device as claimed in claim 11, wherein said freedom giving means reduces said degree of freedom by mapping the appearance time instants given said degree of freedom onto a time axis of sampling instants defined by said sampling frequency.

19. A multipulse encoding device as claimed in claim 18, wherein said freedom giving means gives to the appearance time instants of multipulses the degree of freedom with no changes throughout each analysis frame.

20. A multipulse decoding device for decoding an encoded speech signal produced by a multipulse encoder as a combination of an encoded sequence of modified multipulses and encoded spectrum envelope information by sampling an original speech signal into a sampled speech signal at predetermined sampling frequency defining successive analysis frames, by linear predictive coding (LPC) analyzing the sampled speech signal of each analysis frame for extraction of LPC coefficients and for production of original spectrum envelope information of said original speech signal based on said LPC coefficients, by multipulse analyzing said LPC coefficients into original multipulses having appearance time instants at which said original multipulses appear and multipulse amplitudes in correspondence in each analysis frame to features of excitation source information representative of speech information of said original speech signal in combination with said original spectrum envelope information, by modifying said original multipulses into modified multipulses of a sequence with said appearance time instants given a degree of freedom which allows said appearance time instants to be modified without increasing said predetermined sampling frequency, and by encoding said modified multipulses into said encoded sequence of modified multipulses and said original spectrum envelope information into said encoded spectrum envelope information, said multipulse decoding device comprising:

decoding means for decoding said encoded sequence into a decoded sequence of modified multipulses and said encoded spectrum envelope information into decoded spectrum envelope information; and

multipulse waveform synthesizing means for synthesizing said decoded sequence of modified multipulses and said decoded spectrum envelope information into a synthesized speech signal equivalent to said original speech signal.

21. A multipulse decoding device as claimed in claim 20, wherein said multipulse waveform synthesizing means comprises:

LPC synthesizing means responsive to said decoded spectrum envelope information for processing said decoded sequence of modified multipulses into a plurality of primary synthesized outputs having said sampling frequency in common and phases dependent on differences between said modified and said original multipulses;

upsampling means for upsampling said primary synthesized outputs by a synthesis reference clock signal of a higher frequency than said sampling frequency into secondary synthesized outputs having said higher frequency in common and said phases;

summing means for summing up said secondary synthesized outputs into a sum output of said higher frequency and a predetermined one of said phases; and

D/A converter means for converting said sum output into said synthesized speech signal.

22. A multipulse decoding device as claimed in claim 20, wherein said multipulse waveform synthesizing means comprises:

LPC synthesizing means responsive to said decoded spectrum envelope information for processing said decoded sequence of modified multipulses into a plurality of primary synthesized waveform trains having said sampling frequency in common and phases dependent of difference between said modified and said original multipulses;

up/down sampling means for up sampling said primary synthesized waveform trains responsive to a synthesis reference clock signal of a higher frequency than said sampling frequency to produce upsampled primary synthesized waveform trains which are down sampled in response to timing pulse sequences having said sampling frequency in common and said phases, to generate secondary synthesized waveform trains having said sampling frequency in common and one of said phases that is specified by a predetermined one of said timing pulse sequences;

summing means for summing up said secondary synthesized waveform trains into a sum waveform sequence; and

digital-to-analog (D/A) converter means for converting said sum waveform sequence into said synthesized speech signal.

23. A multipulse decoding device as claimed in claim 20, wherein said multipulse waveform synthesizing means comprises:

discrete pulse generating means by correlation processing of said decoded spectrum envelope information for generating trains of discrete pulses, the discrete pulses of each of said trains having pulse positions corresponding to said modified multipulses, the pulse positions in said trains being different in correspondence to differences between said modified and said original multipulses;

LPC synthesizing means responsive to said decoded spectrum envelope information and said trains of discrete pulses for processing said decoded sequence of modified multipulses into a synthesized waveform sequence; and

D/A converter means for converting said synthesized waveform sequence into said synthesized speech signal.

24. A multipulse analyzer comprising sampling means for sampling an input speech signal into a sampled speech signal at a predetermined sampling frequency defining successive analysis frames, linear predictive coding (LPC) analyzing means for LPC analyzing said sampled speech signal of each analysis frame to extract LPC coefficients and to produce spectrum envelope information based on said LPC coefficients, and multipulse analyzing means for multipulse analyzing said LPC coefficients into a multipulse sequence of multipulses having appearance time instants at which said original multipulses appear and multipulse amplitude in correspondence in each analysis frame to features of excitation source information representative of speech information of said input speech signal in combination with said spectrum envelope information, wherein said multipulse analyzing means comprises freedom giving means for giving a degree of freedom to said appearance time instants, so that said appearance time instants are modified without increasing said predetermined sampling frequency, to modify said multipulses into modified multipulses relative to sampling instants of said sampled speech signal with the appearance time instants given said degree of freedom and with said multipulse amplitudes as they are.

25. A multipulse analyzer as claimed in claim 24, said multipulse analyzing means comprising an impulse response calculator responsive to said LPC coefficients for calculating an impulse response, cross-correlation calculating means for calculating cross-correlation coefficients between said sampled speech signal and said impulse response, and an autocorrelation calculator for calculating autocorrelation coefficients of said impulse response, wherein said freedom giving means comprises a loop comprising:

interpolating means for interpolating said autocorrelation coefficients by a greatest absolute value of maxima and minima of said cross-correlation coefficients into interpolated autocorrelation coefficients; and

correcting means responsive to said interpolated autocorrelation coefficients for correcting said cross-correlation coefficients into corrected cross-correlation coefficients to repeatedly use the greatest absolute value of maxima and minima of said corrected cross-correlation coefficients a predetermined number of times and to use time positions and extremum amplitudes of maxima and minima of said corrected cross-correlation coefficients as the appearance time instants given said degree of freedom and as said multipulse amplitudes.

26. A multipulse analyzer as claimed in claim 25, wherein said interpolating means comprises:

extremum detecting means connected to said correcting means for detecting, in each instance of said predetermined number of times, an extremum of said cross-correlation coefficients by interpolation in at least three samples comprising one of the maxima and the minima of said corrected cross-correlation coefficients and two samples preceding and following one sampling period of said sampling frequency said one of maxima and minima of corrected cross-correlation coefficients; and

amplitude detecting means for detecting, as said greatest absolute value, a greatest absolute amplitude of the extrema detected during said predetermined number of times.

27. A multipulse analyzer as claimed in claim 24, said multipulse analyzing means comprising an impulse response calculator responsive to said LPC coefficients for calculating an impulse response, wherein:

said multipulse analyzing means comprises;

upsampling means for upsampling said sampled speech signal and said impulse response into an upsampled speech signal and an upsampled response at an analysis reference frequency higher than said sampling frequency;

an upsampled cross-correlation calculator for calculating upsampled cross-correlation coefficients between said upsampled speech signal and said upsampled response; and

an upsampled autocorrelation calculator for calculating upsampled autocorrelation coefficients of said upsampled response;

said freedom giving means extracting in response to said upsampled cross-correlation coefficients and said upsampled autocorrelation coefficients the multipulses having the appearance time instants given said degree of freedom and said multipulse amplitudes.

28. A multipulse analyzer as claimed in claim 24, said multipulse analyzing means comprises an impulse response calculator responsive to said LPC coefficients for calculating an impulse response, cross-correlation calculating means for calculating cross-correlation coefficients between said sampled speech signal and said impulse response, and an autocorrelation calculator for calculating autocorrelation coefficients of said impulse response, wherein:

said multipulse analyzing means comprises;

a multiphase processor for multiphase processing a sequence of said cross-correlation coefficients into a plurality of pulse sequences having said sampling frequency in common and different phases; and

a multipulse detector for detecting a plurality of multipulse sequences in response to said autocorrelation coefficients from said pulse sequences, respectively;

said freedom giving means producing in response to said sampled speech signal and said pulse sequences the multipulses having the appearance time instants given said degree of freedom and said multipulse amplitudes.

29. A multipulse analyzer as claimed in claim 28, wherein said freedom giving means comprises:

local synthesis filters for synthesizing said pulse sequences into a plurality of synthesized outputs;

local sampling means for sampling said synthesized outputs into a plurality of sampled trains of samples sampled in concurrency with said sampled speech signal; and

selecting means for selecting, as the multipulses having the appearance time instants given said degree of freedom and said multipulse amplitudes, the samples of one of said sampled trains that has a best S/N ratio with said sampled speech signal used as a signal and with differences between said sampled speech signal and said sampled trains used as noise.

30. A multipulse analyzer as claimed in claim 29, wherein:

said selecting means produces an indicatiohn signal indicative of the samples of said one of sampled trains;

said encoding means using said sampled trains and said indication signal collectively as the excitation source information in which the appearance time instants are given said degree of freedom.

31. A multipulse analyzer as claimed in claim 24, wherein said freedom giving means reduces said degree of freedom by mapping the appearance time instants given said degree of freedom onto a time axis of sampling instants defined by said sampling frequency.

32. A multipulse analyzer as claimed in claim 31, wherein said freedom giving means gives to the appearance time instants of multipulses the degree of freedom with no changes throughout each analysis frame.

33. A multipulse synthesizer for multipulse synthesizing a sequence of modified multipulses and spectrum envelope information produced by a multipulse analyzer by sampling an original speech signal into a sampled speech signal at a predetermined sampling frequency defining successive analysis frames, by linear predictive coding (LPC) analyzing the sampled speech signal of each analysis frame for extraction of LPC coefficients and for production of said spectrum envelope information based on said LPC coefficients, by multipulse analyzing said LPC coefficients into original multipulses having appearance time instants at which said original multipulses appear and multipulse amplitudes in correspondence in each analysis frame to features of excitation source information representative of speech information of said original speech signal in combination with said spectrum envelope information, and by modifying said original multipulses into the modified multipulses of said sequence with said appearance time instants given a degree of freedom which allows said appearance time instants to be modified without increasing said predetermined sampling frequency, said multipulse synthesizer comprising multipulse waveform synthesizing means for synthesizing said sequence of modified multipulses and said spectrum envelope information into a synthesized speech signal equivalent to said original speech signal.

34. A multipulse synthesizer as claimed in claim 33, wherein said multipulse waveform synthesizing means comprises:

LPC synthesizing means responsive to said spectrum envelope information for processing said sequence of modified multipulses into a plurality of primary synthesized outputs having said sampling frequency in common and phases dependent on differences between said modified and said original multipulses;

upsampling means for upsampling said primary synthesized outputs by a synthesis reference clock signal of a higher frequency than said sampling frequency into secondary synthesized outputs having said higher frequency in common and said phases;

summing means for summing up said secondary synthesized outputs into a sum output of said higher frequency and a predetermined one of said phases; and

D/A converter means for converting said sum ought into said synthesized speech signal.

35. A multipulse synthesizer as claimed in claim 33, wherein said multipulse waveform synthesizing means comprises:

LPC synthesizing means responsive to said spectrum envelope information for processing said sequence of modified multipulses into a plurality of primary synthesized waveform trains having said sampling frequency in common and phases dependent on differences between said modified and said original multipulses;

up/down sampling means for up sampling said primary synthesized waveform trains responsive to a synthesis reference clock signal of a higher frequency than said sampling frequency to produce upsampled primary synthesized waveform trains which are down sampled in response to timing pulse sequences having said sampling frequency in common and said phases, to generate secondary synthesized waveform trains having said sampling frequency in common and one of said phases that is specified by a predetermined one of said timing pulse sequences;

summing means for summing up said secondary synthesized waveform trains into a sum waveform sequence; and

digital-to-analog (D/A) converter means for converting said sum waveform sequence into said synthesized speech signal.

36. A multipulse synthesizer as claimed in claim 33, wherein said multipulse waveform synthesizing means comprises:

discrete pulse generating means by correlation processing of said spectrum envelope information for generating trains of discrete pulses, the discrete pulses of each of said trains having pulse positions corresponding to said modified multipulses, the pulse positions in said trains being different in correspondence to differences between said modified and said original multipulses;

LPC synthesizing means responsive to said spectrum envelope information and said trains of discrete pulses for processing said sequence of modified multipulses into s synthesized waveform sequence; and

D/A converter means for converting said synthesized waveform sequence into said synthesized speech signal.