Low-delay low-bit-rate speech coder

Claim 2

A speech coder comprising: a circuit means coupled to receive coefficients a(i) and to generate a low-bit-rate coded residual signal from an original signal S(n); first synthesizing means sensitive to said low-bit-rate coded residual signal for synthesizing a reconstructed residual signal r'(n); inverse filter means sensitive to said reconstructed residual signal r'(n) for generating a reconstructed speech signal s'(n) and short term predictive (STP) adapting means, sensitive to said reconstructed speech signal for deriving the coefficients a(i) for tuning said circuit means.

Claim 3

A speech coder according to claim 1 wherein said derived sets of coefficients are also used to tune said inverse filter means.

Claim 4

A speech coder according to claim 1 or 2 wherein said circuit means includes an adaptive short-term-predictive (STP) filter; a Vector Quantizing Long Term Predictive (VQ/LTP) coder coupled to the (STP) filter; said Vector Quantizing Long Term Predictive (VQ/LTP) coder including: a Long-Term Predictive loop sensitive to the reconstructed residual signal r'(n) for deriving therefrom a predicted residual x(n) signal; subtracting means for subtracting said predicted residual signal x(n) from a residual signal r(n) for deriving an error residual signal e(n) therefrom; and, Vector Quantizing means sensitive to e(n) signal blocks of samples for converting said blocks of samples into lower bit rate data using Vector Quantizing techniques.

Claim 5

A speech coder according to claim 3 wherein said Vector Quantizing means include Pulse Excited Coding means.

Claim 6

A speech coder according to claim 3 wherein said Vector Quantizing means include Code-Excited Linear Predictive coding means.

Claim 7

A speech coder according to claim 3 wherein said Long-Term-Predictive loop includes: a smoothing filter sensitive to r'(n) for deriving a smoothed reconstructed residual r"(n) therefrom; a LTP adapting means sensitive to the reconstructed residual signal r"(n) for deriving tuning parameters b and M where b represents gain and M represents optimum delay; and, a Long-Term-Predictive (LTP) filter the transfer function of which is, in the z domain, equal to b.z -M , connected to said LTP adapting means.

Claim 8

A speech coder according to claim 1 wherein said STP adapting means include: concatenating means for concatenating currently generated reconstructed speech signal samples s'(n) with previously reconstructed samples s'(n-i) wherein i is a predefined integer number; autocorrelation analysis means sensitive to said concatenating means for deriving autocorrelation coefficients R(k) therefrom; and, conversion means for converting said autocorrelation coefficients R(k) into a(i) filter coefficients, whereby said a(i) coefficients are used to tune said circuit means.

Claim 9

A speech coder according to claim 7 wherein said autocorrelation analysis means include computing means for computing the autocorrelation coefficients R(k) according to: ##EQU18## for k=0, . . . ,8.

Claim 10

A speech coder according to claim 8 wherein said autocorrelation analysis means include: a memory array T(k,N); k=0, . . . ,8; N=0, . . . ,20 for storing partial correlation products; first computing means sensitive to each newly generated set of s'(n) samples for computing and storing into said memory array; ##EQU19## for k=0, . . . ,8. second computing means for deriving new R(k) from previous R(k), i.e. R(k) old according to: R(k) new=R(k) old+T(k,0)-T(k,20) for k=0, . . . ,8. shifting means for shifting said memory array contents according to: T(k,N)=T(k,N-1) for N=20, . . . , 1 and k=0, . . . ,8.

Claim 11

A speech coder according to claim 9, wherein said shifting means includes modulo addressing means.

Claim 12

A circuit arrangement for use in a low-delay low bit-rate speech coder having an adaptive Short-Term-Predictive (STP) filter for receiving original speech signal s(n) and coefficients a(i), originally sampled and coded at a high bit rate and decorrelating said original speech signal s(n) into a low-bit-rate coded residual signal, said circuit arrangement comprising: first synthesizing means sensitive to said low-bit-rate coded residual signal for synthesizing a reconstructed residual signal r'(n); inverse filter means sensitive to said reconstructed residual signal r'(n) for generating a reconstructed speech signal s'(n); and, STP adapting means, sensitive to said reconstructed speech signal for deriving the coefficients a(i).

Claim 13

A circuit arrangement for use in a low-delay low bit-rate speech coder having an adaptive Short-Term-Predictive (STP) filter for receiving original speech signal s(n) and coefficients a(i), originally sampled and coded at a high bit rate and decorrelating said original speech signal s(n) into a low-bit-rate coded residual signal, said circuit arrangement comprising: first synthesizing means sensitive to said low-bit-rate coded residual signal for synthesizing a reconstructed residual signal r'(n); inverse filter means sensitive to said reconstructed residual signal r'(n) for generating a reconstructed speech signal s'(n); and, STP adapting means, sensitive to said reconstructed speech signal for deriving the coefficients a(i).