Patent ID: 7925501

Claim:
An orthogonal search method for use in a speech coding, by calculating a search reference value, the orthogonal search method comprising: generating an adaptive codevector representing a pitch component; generating a random codevector representing a random component; generating a synthetic speech signal by a synthesis filter being excited by the adaptive codevector and the random codevector; calculating a distortion between the input speech signal and the synthetic speech signal; and selecting one random codevector that minimizes the distortion, wherein the search reference value is calculated by: computing the power, α=p t H t Hp, of a signal, Hp, obtained by synthesis in the synthesis filter using the adaptive codevector; computing an auto-correlation matrix, A=H t H, of filter coefficients of the synthesis filter; calculating a matrix, M, by providing a time reverse synthesis, r t =p t H t H, to the signal, Hp, obtained by syntheses in the synthesis filter using the adaptive codevector and by taking an outer product, M=rr t , of the resultant signal by the time reverse synthesis; calculating a value, 1/D=1/{c t (αA−M)c}, by using the power α, the auto-correlation matrix A, the matrix M and the random codevector c; and calculating the search reference value using the value 1/D, where p is the adaptive codevector, c is the random codevector, H is the synthesis filter coefficient matrix, and t denotes transpose.