Abstract
Adaptive multi-rate wideband (AMR-WB) speech codecs have been widely used for high speech quality in modern mobile communication systems, e.g., handheld mobile devices. Nevertheless, a major handicap is that a remarkable computational load is required in the vector quantization (VQ) of immittance spectral frequency (ISF) coefficients of an AMR-WB coding. In view of this, a two-stage search algorithm is presented in this paper as an efficient way to reduce the computational complexity of ISF quantization in AMR-WB coding. At stage 1, an input vector is assigned to a search subspace in an efficient manner using the binary search space-structured VQ (BSS-VQ) algorithm, and a codebook search is performed over the subspace at stage 2 using the iterative triangular inequality elimination (ITIE) approach. Through the use of the codeword rejection mechanisms equipped in both stages, the computational load can be remarkably reduced. As compared with the original version of the BSS-VQ algorithm, the upgraded version provides a computational load reduction of up to 51%. Furthermore, this work is expected to satisfy the energy saving requirement when implemented on an AMR-WB codec of mobile devices.
Highlights
The development of the adaptive multi-rate wideband (AMR-WB) speech codec [1,2,3,4] aims to considerably improve the speech quality on handheld mobile devices
As a prerequisite of a vector quantization (VQ) codebook search in the binary search space-structured VQ (BSS-VQ) algorithm, an input vector is assigned in an efficient manner to a subspace, over which a small number of codeword searches is conducted through the combined use of lookup tables and a fast locating technique
A performance comparison is conducted among the equal-variance equal-norm nearest neighbor search (EEENNS), DI-triangular inequality elimination (TIE), iterative triangular inequality elimination (ITIE), and the original and upgraded versions of BSS-VQ
Summary
The development of the adaptive multi-rate wideband (AMR-WB) speech codec [1,2,3,4] aims to considerably improve the speech quality on handheld mobile devices It is an algebraic code-excited linear-prediction (ACELP)-based coding technique [4,5], and is equipped with nine coding modes with bitrates between 6.6 and 23.85 kbps. The speech quality of a smartphone can be improved at the cost of high battery power consumption, using an AMR-WB codec It takes an AMR-WB encoder a tremendous amount of time to quantize immittance spectral frequency (ISF) coefficients in various coding modes [6,7,8,9].
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