Speech coding and decoding methods using adaptive and random code books

A speech coding method in which a speech signal is analyzed by linear prediction in units of frames to obtain predictive coefficients, a weighted sum of vectors from an adaptive codebook having a pitch period component and K random codebooks, K being an integer equal to or greater than 2, is provided as an excitation vector to a synthesis filter of said predictive coefficients to obtain a synthesized speech, and a pitch period, a code of random codevector and a gain are determined which minimize an error between said synthesized speech and an input speech, said method comprising:

• a first step of generating from said adaptive codebook a periodic component codevector P which minimizes distortion of said synthesized speech relative to said input speech;
• a second step of providing all random codevectors from said K random codebooks each having a plurality of random codevectors C.sub.ij and said periodic component codevector P to said synthesis filter to obtain HC.sub.ij and HP, i representing the number of each random codebook, i=0, . . . , K-1, j representing the number of each random codevector in an i.sup.th one of said random codebooks, j=0, . . . , N.sub.i, N.sub.i being an integer equal to or greater than 2 and representing the number of said random codevectors of said i.sup.th random codebook, and H representing an impulse response matrix of said synthesis filter;
• a third step of orthogonalizing said HC.sub.ij and said HP to obtain a reconstructed vector U.sub.ij given by the following equation:
• ##EQU9## where T represents a transposed matrix;
• a fourth step of determining, for each of said K random codebooks, a code J(i) of said random codevector which minimizes distortion d of said reconstructed vector relative to an input speech vector X, said distortion being given by the following equation:
• ##EQU10## where g represents a gain variable;
• and a fifth step of weighting said periodic component codevector and a random codevector C.sub.ij(i) of said code J(i) with gains g.sub.0 and g.sub.1, respectively, and adding together the weighted periodic component codevector and the weighted random codevector, calculating, for a plurality of sets of gains g.sub.0 and g.sub.1, distortion, relative to the input speech vector X, of a synthesized speech which is reconstructed when the result of said accumulation is provided as said excitation vector to said synthesis filter to excite said synthesis filter, said distortion of said synthesized speech vector X relative to said input speech being expressed by ##EQU11## and then determining said set of gains g.sub.0 and g.sub.1 to be coded which minimizes said distortion of said synthesized speech.

A speech coding method in which an input speech is analyzed for each frame, an excitation signal composed of a weighted linear sum of a periodic component codevector of an adaptive codebook and a random codevector of a random codebook is applied to a linear predictive synthesis filter to synthesize a speech, and codevectors are selected so that distortion of said synthesized speech relative to said input speech is minimized, said method comprising:

• generating from a plurality of adaptive codebooks periodic component codevectors rendered repetitious with respective periods;
• updating said periodic component codevector of each of said adaptive codebooks with a weighted linear sum of said plurality of periodic component codevectors and said random codevector from said random codebook;
• and
• generating said excitation signal of the current frame with a new weighted linear sum of said updated periodic component codevectors of said plurality of adaptive codebooks and said random codevector of said random codebook.

A speech coding method in which a speech is reconstructed by driving a linear predictive synthesis filter with a periodic component codevector generated from an adaptive codebook through use of a selected pitch period and a random codevector output from a random codebook, and an input speech is coded for each frame by use of said periodic component codevector and said random codevector so that distortion of said reconstructed speech relative to said input speech is minimized, said method comprising:

• generating a periodic component codevector of an optimum pitch period for said input speech vector on the basis of said excitation vector of the previous frame held in said adaptive codebook;
• multiplying said periodic component codevector by m predetermined window functions to obtain m envelope vectors, multiplying said envelope vectors by m weight elements of weight vectors selected from a weight codebook, and outputting the sum of the results of said multiplications as said periodic component codevector, m being an integer equal to or greater than 2;
• and
• exciting said synthesis filter with said periodic component codevector, searching said weight codebook for a weight vector which minimizes distortion of said reconstructed speech from said synthesis filter relative to said input speech, and determining a weight parameter representing said weight vector.

A speech decoding method in which a speech is reconstructed by exciting a linear predictive filter with an excitation vector obtained by combining a periodic component codevector generated from an adaptive codebook on the basis of a given period code and a random codevector output from a random codebook on the basis of a given random code, said method comprising:

• cutting out an excitation vector of the previous frame in accordance with said period code and repeatedly concatenating said cut-out excitation vector to generate a periodic component codevector;
• reading out from said random codebook a random codevector corresponding to a random code, generating a repetitious random codevector by repeating a vector segment cut out with a pitch period corresponding to said period code, and outputting a repetitious random component vector corresponding to said repetitious random codevector;
• generating an excitation vector by linearly combining said periodic component vector and said repetitious random component vector;
• and
• synthesizing a speech by exciting said linear predictive synthesis filter with said generated excitation vector.