A Fast Method of Calculating High-Order Backward LP Coefficients for Wideband CELP Coders

概要

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This paper proposes a fast method of calculating high-order backward Linear Prediction(LP) coefficients for wideband Code Excited LP(CELP) coders operating at around 16kbit/s. The fast calculation is achieved by a recursive calculation for the high-order autocorrelation of the decoded signal. The recursive calculation can be employed thanks to a novel method of converting the autocorrelation of the decoded signal to that of the residual signal. High-order backward LP coefficients are computed from the autocorrelation of the residual signal using the Levinson-Durbin(LD) procedure. The conversion approximately performs inverse-filtering using LP coefficients representing a corresponding envelope spectrum. Due to the recursive calculation, the proposed fast calculation method achieves 30% to 45% reduction in computations to calculate the high-order backward LP coefficients compared to the conventional method. Subjective tests show that a wideband Multi-Pulse based CELP(MP-CELP) coder at 16kbit/s with the proposed method achieves comparable coding quality to that with the conventional one with 35% reduction in computations needed for calculation of the backward LP coefficients.
社団法人電子情報通信学会の論文
2000-04-25