Patent attributes
A codebook excited linear prediction coding system providing improved digital speech coding for high quality speech at low bit rates with side-by-side codebooks for segments of the modeled input signal to reduce the complexity of the codebook search. A linear predictive filter responsive to an input signal desired to be modeled is used for identifying a basis vector from a first codebook over predetermined intervals as a subset of the input signal. A long term predictor and a vector quantizer provide synthetic excitation of modeled waveform signal components corresponding to the input signal desired to be modeled from side-by-side codebooks by providing codevectors with concatenated signals identified from the basis vector over the predetermined intervals with respect to the side-by-side codebooks. Once a codevector is identified, the codebook at the next segment is searched and a concatenation of codevectors is provided by selecting up to but not including the current segment. The codevector is treated as an additional basis vector for the codebook search at the current segment. It is possible to significantly reduce the complexity of the VSELP codebook search by precomputing and storing the terms for the code search that do not change from segment to segment. Using these techniques, the complexity of searching a 45 bit VSELP codebook (N=40, M=45, M′=9, J=5) was found to be approximately equivalent to searching a traditionally structured 10 bit VSELP codebook (N=40, M=10, J=1). A concatenation of codevectors or carry-along basis vectors are formed as a concatenation of VSELP codevectors selected up to but not including the current segment.
