Multipulse LPC speech processing arrangement

• US 4,701,954 A
• Filed: 03/16/1984
• Issued: 10/20/1987
• Est. Priority Date: 03/16/1984
• Status: Expired due to Term

• Current Assignee: Alcatel-Lucent USA, Inc. (Nokia Corporation)
• Original Assignee: American Telephone & Telegraph (AT&T, Inc.)
• Inventors: Atal, Bishnu S.
• Primary Examiner(s): Kemeny, E. S. Matt
• Application Number:
  US06/590,228
• Time in Patent Office: 1,313 Days
• Field of Search: 381/29-40, 381/49, 381/50, 381/51, 364/513.5, 375/122
• US Class Current: 704/216
• CPC Class Codes: G10L 19/10 the excitation function being a multipulse excitation

Abstract

A multipulse-code approximation of of one frame of a predictive residual signal may lose the frame-to-frame redundancy. Accordingly, pitch redundancy removal during the iterative process of forming the multipulse sequence, rather than frame-to-frame code comparison, provides reduction of excitation signal bit rate, substantially independent of voice pitch. A speech pattern predictive coding arrangement includes forming a prescribed format multipulse excitation signal for each successive time frame of the pattern. The multipulse excitation signal corresponds to the frame predictive residual. The redundancy in the multipulse excitation signal is reduced by forming a signal representative of the similarities between the current frame speech pattern and the speech pattern of preceding frames and removing such similarities from the multipulse excitation signal. Advantageously, the bit rate of the multipulse excitation signal is reduced and the excitation signal is rendered substantially independent of voice pitch.

Claims

1. A method for generating multipulse excitation codes for a speech pattern comprising the steps of:

partitioning a speech pattern into successive time frame portions;

generating a set of predictive parameter signals representative of the speech pattern portion of each successive time frame;

producing a signal representative of the predictive residual of each successive time frame speech pattern portion responsive to the time frame speech parameter signals and time frame speech pattern portion; and

generating a multipulse excitation code having a sequence of n=1, 2, . . . , N pulses for each successive time frame to provide prescribed coded speech pattern quality where N is substantially independent of the pitch of the speech pattern by iteratively forming pulses for said time frame, each pulse having a magnitude β and

a location m within the frame in N successive iterations and each successive iteration including the steps of;

combining said time frame predictive parameter signals with said time frame predictive residual signals to form a signal y(n) corresponding to the time frame speech pattern portion,

combining the excitation pulse sequence of the preceding iteration with said time frame predictive parameter signals to form a signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion,

forming a signal representative of the differences between said signal y(n) corresponding to the time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion,

comparing the current time frame signal representative of the differences between the signal y(n) corresponding to the time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion with the signal of prescribed preceding time frames representative of the differences between said signal y(n) corresponding to the preceding time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the preceding time frame speech pattern portion to generate a signal y_p (n) representative of speech pattern portions of said preceding time frames having a predetermined degree of similarity to the speech pattern portion of the time frame, and

producing an excitation pulse of magnitude β and

location m for the present iteration responsive to the differences between said speech pattern portion representative signal y(n) and the sum of said signal representative of the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion and said signal y_p (n) representative of similar speech pattern portions of said preceding time frames.

2. A method for generating multipulse excitation codes for a speech pattern according to claim 1 further comprising the step of utilizing said frame multiphase excitation code and said frame predictive parameter signals to construct a replica of said frame speech pattern.

3. Apparatus for generating multipulse excitation codes for a speech pattern comprising:

means for partitioning a speech pattern into successive time frame portions;

means for generating a set of predictive parameter signals representative of the speech pattern portion of each successive time frame;

means responsive to the time frame speech parameter signals and time frame speech pattern portion for producing a signal representative of the predictive residual of each successive time frame speech pattern portion; and

means for iteratively forming a sequence of n=1, 2, . . . N pulses for said time frame, each pulse having a magnitude β and

a location m within the frame where N is substantially independent of the pitch of the speech pattern to generate a multiphase excitation code for each successive time frame to provide prescribed coded speech pattern quality;

said iteratively pulse sequence forming means comprises means for generating the nth pulse of said sequence including;

means for combining said time frame predictive parameter signals with said time frame predictive residual signal to form a signal y(n) corresponding to the time frame speech pattern portion,

means for combining the excitation pulse sequence of the preceding iteration with said time frame predictive parameter signals to form a signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion,

means for forming a signal representative of the differences between said signal y(n) corresponding to the time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion,

means for comparing the signal of the current time frame representative of the differences between said signal y(n) corresponding to the time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion of the current time frame with the signal of prescribed preceding time frames representative of the differences between said signal y(n) corresponding to the preceding time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the preceding time frame speech pattern portion to generate a signal y_p (n) representative of portions of said preceding time frames having a predetermined degree of similarity to the speech pattern portion of the time frame,

means for forming a signal representative of the sum of said signal representative of the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion and said signal y_p (n) representative of similar portions of said preceding time frames, and

means responsive to the differences between said speech pattern portion representative signal y(n) and the sum of said signal representative of the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion and said signal y_p (n) representative of similar portions of said preceding time frames for producing an excitation pulse of magnitude β and

location m for the present iteration.

4. Apparatus for generating multipulse excitation codes for a speech pattern according to claim 3 further comprising means for utilizing said frame multipulse excitation code and said frame predictive parameter signals to construct a replica of said frame speech pattern.

5. A speech processor for producing a speech message comprising:

means for receiving a sequence of speech message time frame signals, each speech time frame signal including a set of predictive speech parameter signals, a first coded excitation signal, and a second coded excitation signal for said time frames;

means for combining said first and second coded excitation signal to form a multipulse speech message excitation representative signal for the frame; and

means jointly responsive to said linear predictive frame speech parameter signals and said frame multipulse excitation representative signal for generating a speech pattern corresponding to the speech message;

the first coded excitation signal for said frame being formed by the steps of;

generating a sequence of signals corresponding to successive samples of a speech pattern;

partitioning a speech pattern into successive time frame portions;

generating a set of predictive parameter signals representative of the speech pattern portion of each successive time frame;

producing a signal representative of the predictive residual of each successive time frame speech pattern portion responsive to the time frame speech parameter signals and time frame speech pattern portion; and

generating a multipulse excitation code having a sequence of n=1, 2, . . . , N pulses for each successive time frame to provide prescribed coded speech pattern quality where N is substantially independent of the pitch of the speech pattern by iteratively forming a sequence of pulses for said time frame, each pulse having a magnitude β and

a location m within the frame in N successive iterations and each successive iteration including the steps of;

combining said time frame predictive parameter signals with said time frame predictive residual signals to form a signal y(n) corresponding to the time frame speech pattern portion,

combining the excitation pulse sequence of the preceding iteration with said time frame predictive parameter signals to form a signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion,

forming a signal representative of the differences between said signal y(n) corresponding to the time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion,

comparing the current time frame signal representative of the differences between said signal y(n) corresponding to the time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion with the signal of prescribed preceding time frames representative of the differences between said signal y(n) corresponding to the preceding time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the preceding time frame speech pattern portion to generate a signal y_p (n) representative of speech pattern portions of said preceding time frames having a predetermined degree of similarity the speech pattern portion of the time frame, and

producing an excitation pulse of magnitude β and

location m for the present iteration responsive to the differences between said speech pattern portion representative signal y(n) and the sum of said signal representative of the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion and said signal y_p (n) representative of similar speech pattern portions of said preceding time frames.

6. A method for producing a speech message comprising:

receiving a sequence of speech message time frame signals, each speech time frame signal including a set of linear predictive speech parameter signals, a first coded excitation signal, and a second coded excitation signal for said time frame;

forming a multipulse speech message excitation representative signal for the frame responsive to said first and second coded excitation signals, and

generating a speech pattern corresponding to the speech message jointly responsive to said frame linear speech parameter signals and said frame multipulse excitation representative signal;

the first coded excitation signal for said frame being formed by the steps of;

partitioning a speech pattern into successive time frame portions;

generating a set of predictive parameter signals representative of the speech pattern portion of each successive time frame;

producing a signal representative of the predictive residual of each successive time frame speech pattern portion responsive to the time frame speech parameter signals and time frame speech pattern portion; and

generating a multipulse excitation code having a sequence of n=1, 2, . . . , N pulses for each successive time frame to provide prescribed coded speech pattern quality where N is substantially independent of the pitch of the speech pattern by iteratively forming a sequence of pulses for said time frame, each pulse having a magnitude β and

a location m within the frame in successive iterations and each successive iteration including the steps of;

combining said time frame predictive parameter signals with said time frame predictive residual signals to form a signal y(n) corresponding to the time frame speech pattern portion,

combining the excitation pulse sequence of the preceding iteration with said time frame predictive parameter signals to form a signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion,

forming a signal representative of the differences between said signal y(n) corresponding to the time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion,

comparing the current time frame signal representative of the differences between said signal y(n) corresponding to the time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion of the current time frame with the signal of prescribed preceding time frames representative of the differences between said signal y(n) corresponding to the preceding time frame speech pattern portion and said signal z(n) corresponding to the contribution of the preceding iteration excitation pulse sequence to the preceding time frame speech pattern portion to generate a signal y_p (n) representative of speech pattern portions of said preceding time frames having a predetermined degree of similarity to the speech pattern portion of the time frame, and

producing an excitation pulse of magnitude β and

location m for the present iteration responsive to the differences between said speech pattern portion representative signal y(n) and the sum of said signal representative of the contribution of the preceding iteration excitation pulse sequence to the time frame speech pattern portion and said signal y_p (n) representative of similar speech pattern portions of said preceding time frames.