Patent ID: 6810381
Filing Date: 2004-10-26
Classification: G10L

Abstract:
An audio coding method for encoding an input acoustic signal by generating a synthesized acoustic signal through the use of codebook means and searching said codebook means for indices which will minimize an error between said input acoustic signal and said synthesized acoustic signal, said method comprising the steps of:(a) estimating said synthesized acoustic signal for said input acoustic signal; (b) determining, from at least one of said input acoustic signal and said estimated synthesized acoustic signal, coefficients of a p-th order first LP synthesis filter and coefficients of a cascade-connected synthesis filter composed of a pâ€²-th order second LP synthesis filter and an n-th order third LP synthesis filter, said order pâ€² being equal or nearly equal to said order p and said order n being higher than said order p; (c) estimating, as first and second excitation signals for driving said first LP synthesis filter and said cascade-connected synthesis filter, respectively, first and second residual signals obtained by inverse filtering of said estimated synthesized acoustic signal by a first inverse filter of an inverse characteristic to said first LP synthesis filter and a second inverse filter of an inverse characteristic to said cascade-connected synthesis filter; (d) determining from said first and second excitation signals which of said first LP synthesis filter and said cascade-connected synthesis filter will provide higher coding quality, and based on the result of determination, selecting, as a synthesis filter for audio coding, that one of said first LP synthesis filter and said cascade-connected synthesis filter which will provide higher coding quality; (e) providing a gain to an excitation vector selected from codebook means to obtain an excitation signal, generating a synthesized acoustic signal by applying said excitation signal to that one of said first LP synthesis filter and said cascade-connected synthesis filter selected as said synthesis filter for audio coding, and computing an error between said input acoustic signal and said synthesized acoustic signal; (f) determining said excitation vector and said gain which will minimize said error between said synthesized acoustic signal generated by repeating said step (e); and (g) outputting at least codebook indices representing said determined excitation vector, a gain index representing said determined gain and a mode code representing which one of said first LP synthesis filter and said cascade-connected synthesis filter has been selected.