Algebraic code-excited linear prediction speech coding method

• US 5,717,825 A
• Filed: 08/26/1996
• Issued: 02/10/1998
• Est. Priority Date: 01/06/1995
• Status: Expired due to Term

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Lamblin, Claude
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): OPSASNICK, MICHAEL N
• Application Number:
  US08/682,721
• Time in Patent Office: 533 Days
• Field of Search: 395/2.09, 395/2.1, 395/2.28, 395/2.29, 395/2.3, 395/2.32
• US Class Current: 704/223
• CPC Class Codes: G10L 19/107 Sparse pulse excitation, e.g. by using algebraic codebook
• CPC Class Codes: G10L 2019/0008 Algebraic codebooks
• CPC Class Codes: G10L 2019/0014 Selection criteria for distances

Abstract

The method uses the technique of CELP coding with algebraic codebook. The search for the CELP excitation includes a calculation of certain components of the covariance matrix U=H^T ·H where H denotes a lower triangular Toeplitz matrix formed on the basis of the impulse response of a compound filter made up of synthesis filters and of a perceptual weighting filter. The memory-stored components of the covariance matrix are only those of the form U(pos_i,p,pos_i,p) and those of the form U(pos_i,p, pos_j,q), pos_i,p and pos_j,q respectively denoting position i and position j for the pulses p and q in the codes of the algebraic codebook.

Claims

1. In a code-excited linear prediction (CELP) speech coding method, comprising the steps of:

digitizing a speech signal as successive frames of L samples;

adaptively determining synthesis parameters defining synthesis filters, and excitation parameters including, for each frame, pulse positions in an excitation code of L samples belonging to a predetermined algebraic codebook and an associated excitation gain; and

transmitting quantization values representative of the determined parameters, wherein the algebraic codebook is defined on the basis of at least one group of N sets of possible pulse positions in codes of at least L samples, a code from the codebook being represented by N pulse positions belonging respectively to the N sets of positions of a group, wherein determining the excitation parameters relating to a frame includes selecting a code from the codebook which maximizes a quantity P_k² /α

_k², in which P_k =D·

c_k^T denotes the scalar product of a code c_k from the codebook and a target vector D depending on the speech signal of the frame and on the synthesis parameters, and α

_k² denotes the energy in the frame of the code c_k filtered by a compound filter made up of the synthesis filters and a perceptual weighting filter, calculating the energies α

_k² including calculating and storing in a memory components of a covariance matrix U=H^T ·

H, where H denotes a lower triangular Toeplitz matrix with L rows and L columns, formed from the impulse response h(0), h(1), . . . , h(L-1) of said compound filter;

the improvement comprising, for at least one group of N sets, storing in the memory only those components of the covariance matrix which are of the form;

##EQU16## with 0≦

p<

N and those which are of the form;

##EQU17## pos_i,p and pos_j,q respectively denoting the positions of order i and j in the sets of said group containing possible positions for the pulses p and q of the codes from the codebook.

2. The improvement of claim 1, wherein, for a group of N sets, said memory-stored components of the covariance matrix are structured in the form of N correlation vectors and N(N-1)/2 correlation matrices, each correlation vector R_p,p being associated with a pulse number p in the codes from the codebook (0≦

p<

N) and being of dimension L_p '"'"' equal to the cardinal of the set from said group which contains possible positions for the pulse p, with components i (0≦

i<

L_p '"'"') of the form R_p,p (i)=U(pos_i,p,pos_i,p), and each correlation matrix R_p,q being associated with two different pulse numbers p,q in the codes from the codebook (0≦

p<

q<

N) and having L_p '"'"' rows and L_q '"'"' columns with components of the form R_p,q (i,j)=U(pos_i,p,pos_j,q) in row i and in column j (0≦

i<

L_p '"'"' and 0≦

j<

L_q '"'"').

3. The improvement of claim 2, wherein the sets of said group which contain possible positions for a pulse of the codes from the codebook all have the same cardinal L'"'"', the position of order i in the set of the possible positions for the pulse p (0≦

i<

L'"'"', 0≦

p<

N) being given by;

space="preserve" listing-type="equation">pos.sub.i,p =δ

·

(iN+p)+ε

,

δ and

ε

being two integers such that δ

>

0 and ε

≧

0.

4. The improvement of claim 3, wherein the calculation of the N correlation vectors relating to a group comprises an initialization of an integer variable k and of an accumulation variable cor, and a loop indexed by an integer i decreasing from L'"'"'-1 to 0, the iteration i in said loop comprising the successive calculations of the components R_p,p (i) of said vectors for p decreasing from N-1 to 0, a component R_p,p (i) being taken equal to the accumulation variable cor after δ

incrementations of the integer variable k and δ

corresponding additions of the terms h(k)·

h(k) to the accumulation variable cor.

5. The improvement of claim 3, wherein the calculation of the N(N-1)/2 correlation matrices relating to a group comprises, for every integer t in the interval 1,N-1! and every integer d'"'"' in the interval 0,L'"'"'-1!, an initialization of an integer variable k and of an accumulation variable cor, and a loop indexed by an integer i decreasing from L'"'"'-1-d'"'"' to 0, the iteration i in said loop comprising the successive calculations of the components R_p,p+t (i,i+d'"'"') of said matrices for p decreasing from N-1-t to 0 and then, if i>

0, the successive calculations of the components R_q,q+N-t (i+d'"'"',i-1) of said matrices for q decreasing from t-1 to 0, a component R_p,p+t (i,i+d'"'"') or R_q,q+N-t (i+d'"'"',i-1) being taken equal to the accumulation variable cor after δ

incrementations of the integer variable k and δ

corresponding additions of the terms h(k)·

h(k+d) to the accumulation variable cor, with d=δ

·

(t+d'"'"'N).

6. The improvement of claim 2, wherein the algebraic codebook is defined on the basis of M groups of N sets of L'"'"' possible positions for a pulse of a code from the codebook, with M>

1, the position of order i in the set of the group m containing the possible positions for the pulse p (0≦

i<

L'"'"', 0≦

m<

M, 0≦

p<

N) being given by;

space="preserve" listing-type="equation">pos.sub.i,p.sup.(m) =δ

·

(iN+p)+ε

.sup.(m)

δ

, ε

.sup.(0), . . . , ε

.sup.(M-1) being integers such that 0≦

ε

.sup.(0) <

. . . <

ε

.sup.(M-1) <

δ

.

7. The improvement of claim 6, wherein the correlation vectors and the correlation matrices are stored in memory only for μ

of the groups, μ

being an integer such that 1≦

μ

<

M.

8. The improvement of claim 7, wherein the calculation of the N correlation vectors relating to a group comprises an initialization of an integer variable k and of an accumulation variable cor, and a loop indexed by an integer i decreasing from L'"'"'-1 to 0, the iteration i in said loop comprising the successive calculations of the components R_p,p (i) of said vectors for p decreasing from N-1 to 0, a component R_p,p (i) being taken equal to the accumulation variable cor after δ

incrementations of the integer variable k and δ

corresponding additions of the terms h(k)·

h(k) to the accumulation variable cor.

9. The improvement of claim 7, wherein the calculation of the N(N-1)/2 correlation matrices relating to a group comprises, for every integer t in the interval 1, N-1! and every integer d'"'"' in the interval 0, L'"'"'-1!, an initialization of an integer variable k and of an accumulation variable cor, and a loop indexed by an integer i decreasing from L'"'"'-1-d'"'"' to 0, the iteration i in said loop comprising the successive calculations of the components R_p,p+t (i,i+d'"'"') of said matrices for p decreasing from N-1-t to 0 and then, if i>

0, the successive calculations of the components R_q,q+N-t (i+d'"'"',i-1) of said matrices for q decreasing from t-1 to 0, a component R_p,p+t (i,i+d'"'"') or R_q,q+N-t (i+d'"'"',i-1) being taken equal to the accumulation variable cor after δ

incrementations of the integer variable k and δ

corresponding additions of the terms h(k)·

h(k+d) to the accumulation variable cor, with d=δ

·

(t+d'"'"'N).

10. The method for code excited linear prediction (CELP) speech coding according to claim 9, wherein the N correlation vectors are calculated for at least two groups in said loop indexed by i.

11. The improvement of claim 6, wherein the calculation of the N correlation vectors relating to a group comprises an initialization of an integer variable k and of an accumulation variable cor, and a loop indexed by an integer i decreasing from L'"'"'-1 to 0, the iteration i in said loop comprising the successive calculations of the components R_p,p (i) of said vectors for p decreasing from N-1 to 0, a component R_p,p (i) being taken equal to the accumulation variable cor after δ

incrementations of the integer variable k and δ

corresponding additions of the terms h(k)·

h(k) to the accumulation variable cor.

12. The improvement of claim 6, wherein the calculation of the N(N-1)/2 correlation matrices relating to a group comprises, for every integer t in the interval 1, N-1! and every integer d'"'"' in the interval 0,L'"'"'-1!, initialization of an integer variable k and of an accumulation variable cor, and a loop indexed by an integer i decreasing from L'"'"'-1-d'"'"' to 0, the iteration i in said loop comprising the successive calculations of the components R_p,p+t (i,i+d'"'"') of said matrices for p decreasing from N-1-t to 0 and then, if i>

0, the successive calculations of the components R_q,q+N-t (i+d'"'"',i-1) of said matrices for q decreasing from t-1 to 0, a component R_p,p+t (i,i+d'"'"') or R_q,q+N-t (i+d'"'"',i-1) being taken equal to the accumulation variable cor after δ

incrementations of the integer variable k and δ

corresponding additions of the terms h(k)·

h(k+d) to the accumulation variable cor, with d=δ

·

(t+d'"'"'N).

13. The method for code excited linear prediction (CELP) speech coding according to claim 12, wherein the N(N-1)/2 correlation matrices are calculated for at least two groups in said loops indexed by i.