Efficient CELP vocoder and method

Claim 1

An apparatus (220, 220′) for coding a frame of speech comprising N successive samples n=1 to n=N of input analog speech, to determine an optimum codebook vector C k=j (n) which best synthesizes the speech frame, comprising: an adaptive codebook (155) containing K possible perceptually weighted excitation vectors C k (n), where k is an integer index running from 1 to K for identifying the vectors, and n=1 to n=N is the integer index identifying the successive speech samples within the frame of speech; one or more LPC filters (190, 195, 200, 205, 170, 145, 175, 150) for synthesizing trial replicas of the frame of speech when excited by the codebook vectors C k (n) , wherein the LPC filter (190, 195, 200, 205, 170, 145, 175, 150) has an impulse response H(n); means (150) for generating a perceptually weighted target speech residual X(n) for comparison to the results of exciting the one or more LPC filters (190, 195, 200, 205, 170, 145, 175, 150) with the codebook vectors C k (n) to determine the optimum codebook vector C k=j (n) which best synthesizes the speech frame; means (510′) for convolving X(n) with H(n) for each value of n once per frame to produce a convolved output (512′) for delivery to a cross-correlator (520′); means (520′) for cross-correlating the convolved output (512′) with C k (n) for each value of n and k to produce a cross-correlated output (551′) for delivery to a squarer (525′) whose output (521′) is coupled to a divider means (530′); means (560′) for auto-correlating C k (n) for each value of n and k to provide a first auto-correlation output (561′) for delivery to a multiplier means (543′); means (550′) for auto-correlating H(n) to produce a second auto-correlated output (552′, 556′) for delivery to the multiplier means (543′); means (543′) for multiplying the first (561′) and second (552′) autocorrelation outputs to produce an output product (545′) for delivery to an adder (540′); means (540′) for summing the product for each value of k to produce a summed output (541′) for delivery to the divider (530′); divider means (530′) for finding the ratio of the squared cross-correlation output (521′) and the adder summed output (541′) for delivery to a selector means (570′) ; and means (570′) for selecting that value C k=j (n) of C k (n) which produces the greatest magnitude of output from the divider means (530′), for delivery to a channel coder (210).

Claim 2

A method for coding a frame of speech comprising N successive samples of input analog speech and using an adaptive codebook (155) containing K target perceptually weighted excitation vectors C k (n), where k is an integer index running from 1 to K, and n is another integer index identifying successive speech samples n=1, ..., n=N within the frame of speech, to determine an optimum codebook vector C k=j (n) which best synthesizes the speech frame, comprising; providing one or more LPC filters (190, 195, 200, 205, 170, 145, 175, 150) for synthesizing trial replicas of the frame of speech when excited by the codebook C k (n) vectors, wherein the one or more LPC filter (190, 195, 200, 205, 170, 145, 175, 150) has an impulse response H(n); providing a perceptually weighted target speech residual X(n) for comparison to the results of exciting the one or more LPC filters (190, 195, 200, 205, 170, 145, 175, 150) with the codebook vectors C k (n) ; convolving X(n) with H(n) for each value of n once per frame to produce a convolved output W(n) for delivery to a cross-correlator (520′); cross-correlating the convolved output W(n) with C k (n) for each value of n and k to produce a cross-correlated output for delivery to a squarer (525′) whose output is coupled to a divider (530′); auto-correlating C k (n) for each value of n and k to provide a first auto-correlation output U k (m) where m is a dummy index running from m=0 to m=N-1 for delivery to a multiplier (543′); auto-correlating H(n) to produce a second auto-correlated output ⌀(m) where m is a dummy index running from m=0 to m=N-1 for delivery to the multiplier (543′); multiplying the first and second autocorrelation outputs in the multiplier (543′) to produce an output product (545′) for delivery to a summer (540′); summing the product for each value of k to produce a summed output (541′) for delivery to the divider (530′); dividing to obtain the ratio of the squared cross-correlation output (521′) and the adder summed output (541′) for delivery to a peak selector (570′); and selecting in the peak selector that value C k=j (n) of C k (n) which produces the greatest magnitude of output from the divider (530′), for delivery to a channel coder (210).

Claim 3

A method for providing CELP coding for a frame of digitized input speech based on use of a codebook (155) containing K vectors each having N entries, comprising: autocorrelating the codebook vectors for a first P of N entries (P << N) to determine first autocorrelation values (561′) therefore; evaluating the K codebook vectors by producing synthetic speech using the K codebook vectors and the first autocorrelation values and comparing the result to the input speech; determining which S of K codebook vectors (S << K) provide synthetic speech having less error compared to the input speech than the K-S remaining vectors evaluated; autocorrelating the codebook vectors for those S of K vectors for R entries (P < R ≦ N) in each codebook vector to provide second autocorrelation values therefore; re-evaluating the S of K vectors using the second autocorrelation values to identify which of the S codebook vectors provides the least error compared to the input speech; and forming the CELP code for the frame of speech using the identity of the codebook vector providing the least error.

Claim 6

An apparatus (100, 220, 220′, 600) for CELP coding of speech employing autocorrelation coefficients of vectors of an adaptive codebook (155) wherein analysis initially utilizes a subset of samples M in connection with a speech analysis frame of length L > M, comprising: means (610) for determining autocorrelation coefficients U k′ (m) of a first vector C k (n) of length M, where k = 1 and m is an autocorrelation lag index and n is an index of successive samples in the codebook vector, according to a first equation, for m = 0 to T < M; means (624, 626, 628, 630) for determining autocorrelation coefficients U k (m) of remaining codebook vectors incrementally where k ≧ 2 according to a second equation, U′ k (m) = [U′ k-1 (m) + C k (M+k-1)C k (M+k-1+m)] for m = 0 to T < M until (M+k-1)=L; means (632) for scaling the result of the first equation according to U₁(m) = ( L M )U′₁(m) , and scaling the result of the second equation according to U k (m) = ( L M+k-1 )U′ k (m) for m = 0 to T < M to produce a result for each m and each k; and means (220, 220′) for using the result to evaluate which codebook vector provides a least error compared to input speech.

Claim 7

A method for CELP coding speech employing autocorrelation coefficients of vectors of an adaptive codebook (155) of vector length N wherein analysis initially utilizes a subset of samples M < N with a speech analysis frame of length L, comprising: calculating autocorrelation coefficients U k (m) of a first vector C k (n) of length M, where k = 1 and m is an autocorrelation lag index and n is an index of the successive samples in the codebook vector, according to, U₁(m) = ( L M )U′₁(m) for m = 0 to T < M; calculating the autocorrelation coefficients U k (m) of the remaining codebook vectors incrementally where k ≧ 2 according to, U′ k (m) = [U′ k-1 (m) + C k (M+k-1)C k (M+k-1+m)] U k (m) = ( L M+k-1 )U′ k (m) for m = 0 to T < M; repeating the second calculating step until (M+k-1) = L; and using the above-determined autocorrelation coefficients in determining which of the codebook vectors C k (n) produces the least error when compared to input speech.

Claim 8

The method of claims 6 and 7 wherein T = M-1.

Claim 9

A method for CELP coding speech employing autocorrelation coefficients of vectors of an adaptive codebook (155) identified by an index k, wherein analysis by synthesis initially utilizes M < L codebook values where L is the speech analysis frame length and m is an index running from 0 to M-1 describing the autocorrelation lag, comprising: calculating m=0 to M-1 autocorrelation coefficients of a first codebook vector k having n = 1 to M values therein where n is an index of the code vector values; placing the m=0 to M-1 calculated autocorrelation coefficients in a temporary store (630); scaling the coefficients in the temporary store by a multiplying factor L/M and transferring the result to an output (634); multiplying codebook values for n=M+j where j=1 by codebook values for n = M+j down to n = 1 and adding the products to the m=0 to M-1 autocorrelation coefficients, respectively, from the temporary store (630) to produce a result; replacing the autocorrelation coefficients in the temporary store (630) by the result; scaling the coefficients in the temporary store (630) by a multiplying factor L/(M+j) and transferring the result to the output (634); repeating the multiplying, replacing, scaling and transferring steps for j=2 to j=k-1 and k=(L+1-M); and using the autocorrelation coefficients transferred to the output to determining which of the codebook vectors provides better CELP coding of speech.

Claim 10

An apparatus (100, 700) for CELP coding speech by combining a first vector with a set of second vectors identified by an index k, wherein the first and second vectors have values identified by indices n running from n=1 to N, comprising: a first N by N multiplexer (704) having n=1 to N outputs, n=1 to N first inputs, a second input, and n=1 to N select means, wherein a first logic level presented to n th select means couples the n th output to the n th first input and a second logic level presented to the n th select means couples the n th output to the second input; first means for supplying n=1 to N values of the first vector to the n=1 to N first inputs (701) of the first multiplexer (704); means (706) for presenting n=1 to N values of the second vector of index k=1 to the n=1 to N select means (708) of the first multiplexer (704), the second vector providing at the n=1 to N select means the first logic level for some values of n and the second logic level for other values of n; first accumulator means (712) coupled to the first multiplexer output (710) for adding together values of the first vector transferred to the outputs (710) of the first multiplexer (704) to provide a first sum (716); means (714) for indexing k from k=1 to k=K; and means (228) for synthesizing speech based on whichever sum identifies a second vector giving the closest match to target speech.

Claim 12

An apparatus for CELP coding speech using a combination of a first vector V(n) having values identified by index n running from n=1 to N, and a set of second vectors S k (n) wherein each of the second vectors is identified by index k and wherein each of the second vectors has up to N values which are either zero or non-zero and are identified by index n from n=1 to N, comprising: means (704, 706) for identifying indices n k,i of S k (n) for different k wherein S k (n i ) are non-zero; means (712, 721) for adding values of the V(n) corresponding to indices n k,i to form sums Q(k); means (714) for identifying the value k=j corresponding to the largest value Q(k=j); and means (228) for synthesizing speech using S k=j (n).

Claim 15

A method for CELP coding speech by combining a first vector (701) with a set of second vectors identified by index k, wherein the first and second vectors have values identified by indices n running from n=1 to N, comprising: providing an N by N first multiplexer (704) having n=1 to N outputs, n=1 to N first inputs, second inputs, and n=1 to N select means, wherein a first logic level presented to n th select means couples the n th output to the n th first input and a second logic level presented to the n th select means couples the n th output to the second input; supplying n=1 to N values of the first vector (701) to the n=1 to N first inputs of the first multiplexer; presenting n=1 to N values of the second vector (702) of index k=1 to n=1 to N select means of the first multiplexer (704), the second vector providing at the n=1 to N select means the first logic level for some values of n and the second logic level for other values of n; adding together values of the first vector coupled to the first multiplexer output to provide a sum; repeating the presenting and adding steps for further values of k; and synthesizing speech based on whichever sum identifies a second vector giving the closest match to target speech.

Claim 17

A method for CELP coding speech using a combination of a first vector V(n) having values identified by index n running from n=1 to N, and a set of second vectors S k (n) wherein each of the second vectors is identified by index k and wherein each of the second vectors has up to N values which are either zero or non-zero and are identified by index n from n=1 to N, comprising: identifying indices n k,i of S k (n) for different k wherein S k (n i ) are non-zero; adding values of the V(n) corresponding to indices n k,i to form sums Q(k); identifying the value k=j corresponding to the largest value Q(k=j); and synthesizing speech using S k=j (n).