Patent ID: 6243673
Filing Date: 2001-06-05
Classification: G10L

Abstract:
A speech coding apparatus, comprising:a generator that generates a pitch reproduced excitation pulse sequence that simulates a pitch on a current subframe using an excitation pulse sequence generated on a last subframe at a first search operation, while generating said pitch reproduced excitation pulse sequence at subsequent searches using an excitation pulse sequence obtained at a just prior search operation;a linear predictive synthesis filter that obtains a convolution calculation result by performing a convolution calculation using setting coefficients that include linear predictive coefficients, obtained by performing a linear predictive analysis on a speech input signal, perceptual weighted coefficients, used in performing perceptual weighting on said speech input signal, and said pitch reproduced excitation pulse sequence;a memory that stores said convolution calculation result obtained by said linear predictive synthesis filter;an adaptive codebook that stores previously generated excitation pulse sequences as adaptive vectors;a pitch predictive filter that reads an adaptive vector from said adaptive codebook, said pitch predictive filter outputting a multiplication result obtained by multiplying said convolution calculation result by said read adaptive vector;a detector that detects an error between each output multiplication result and a pitch residual signal, when said adaptive vector is sequentially read from said adaptive codebook while a position of said adaptive vector to be read is varied, said detector detecting a read position that minimizes said error as an optimal pitch length; anda controller that controls, at said first search operation, a storing in said memory of first to Nth convolution calculation results corresponding to first to Nth excitation pulse sequences, said first to Nth excitation pulse sequences being obtained by sequentially shifting one sample, said stored first to Nth convolution calculation results being provided to said pitch predictive filter, while at subsequent search operations, said controller controls a storing of a convolution calculation result corresponding to a temporary excitation pulse sequence temporarily generated at said just prior search operation and provides current first to Nth convolution calculation results to said pitch predictive filter, said current first to Nth convolution calculation results comprising a convolution calculation result calculated in a current search operation as a first convolution calculation result and first to N-1th convolution calculation results stored in said memory as a second to Nth convolution calculation, wherein said linear predictive synthesis filter performs said convolution calculation N times, corresponding to the first to Nth excitation pulse sequences obtained by sequentially shifting said one sample, at said first search operation, while performing a single convolution calculation, corresponding to one excitation pulse sequence, at said subsequent search operations.