Abstract
The adaptive multi-rate wideband (AMR-WB) speech codec is widely used in modern mobile communication systems for high speech quality in handheld devices. Nonetheless, a major disadvantage is that vector quantization (VQ) of immittance spectral frequency (ISF) coefficients takes a considerable computational load in the AMR-WB coding. Accordingly, a binary search space-structured VQ (BSS-VQ) algorithm is adopted to efficiently reduce the complexity of ISF quantization in AMR-WB. This search algorithm is done through a fast locating technique combined with lookup tables, such that an input vector is efficiently assigned to a subspace where relatively few codeword searches are required to be executed. In terms of overall search performance, this work is experimentally validated as a superior search algorithm relative to a multiple triangular inequality elimination (MTIE), a TIE with dynamic and intersection mechanisms (DI-TIE), and an equal-average equal-variance equal-norm nearest neighbor search (EEENNS) approach. With a full search algorithm as a benchmark for overall search load comparison, this work provides an 87% search load reduction at a threshold of quantization accuracy of 0.96, a figure far beyond 55% in the MTIE, 76% in the EEENNS approach, and 83% in the DI-TIE approach.
Highlights
With a 16 kHz sampling rate, the adaptive multi-rate wideband (AMR-WB) speech codec [1,2,3,4] is one of the speech codecs applied to modern mobile communication systems as a way to remarkably improve the speech quality on handheld devices
The algebraic code-excited linear-prediction (ACELP)-based technique is developed as an excellent speech coding technique, having a double advantage of low bit rates and high speech quality, but a price paid is a high computational complexity required in an AMR-WB codec
This paper presents a binary search space-structured VQ (BSS-VQ) codebook search algorithm for immittance spectral frequency (ISF) vector quantization in the AMR-WB speech codec
Summary
With a 16 kHz sampling rate, the adaptive multi-rate wideband (AMR-WB) speech codec [1,2,3,4] is one of the speech codecs applied to modern mobile communication systems as a way to remarkably improve the speech quality on handheld devices. The AMR-WB is a speech codec developed on the basis of an algebraic code-excited linear-prediction (ACELP) coding technique [4,5], and provides nine coding modes with bitrates of 23.85, 23.05, 19.85, 18.25, 15.85, 14.25, 12.65, 8.85, and 6.6 kbps. The ACELP-based technique is developed as an excellent speech coding technique, having a double advantage of low bit rates and high speech quality, but a price paid is a high computational complexity required in an AMR-WB codec. Using an AMR-WB speech codec, the speech quality of a smartphone can be improved but at the cost of high battery power consumption. The VQ structure in AMR-WB adopts a combination of a split VQ (SVQ) and a multi-stage VQ (MSVQ)
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