Enhancing the EVRC half rate by the algebraic VQ-CELP

Abstract

This paper presents some update improvement in an algebraic vector quantized codebook excited linear prediction (AVQ-CELP) speech codec. The objective is to enhance the half rate mode of the enhanced variable rate codec (EVRC). In the AVQ-CELP scheme, only the perceptually important components are encoded, and the selection of the components is done in a way similar to the ACELP. A closed-loop procedure is used to select the sub-vectors. The overlapping between the selected vectors are allowed to prevent the pitch peak splitting. The selected sub-vectors are concatenated and vector quantized. An analysis-by-synthesis strategy is used to determine the optimal excitation. The generalized Lloyd algorithm (GLA) is used to optimize the AVQ codebook. In order to improve the synthesis quality of voiced frames, ACELP is used in the strong voiced frames. The proposed algorithm was incorporated in the Nokia CDMA handset prototype. The field testing results indicate a considerable improvement relative to the standard EVRC operating at the maximum half-rate.