MPEG-4 HE-AAC音訊壓縮標準之研究及其在Trimedia DSP上之實作探討
A Study on MPEG-4 HE-AAC and Its Implementation Issues on Trimedia DSPs
Date Issued
2006
Date
2006
Author(s)
Wu, Chi-Hao
DOI
en-US
Abstract
The state-of-the-art audio coding standard, MPEG-4 HE-AAC, achieves high coding efficiency by the employment of Spectral Band Replication (SBR) technique. Comparing with conventional AAC, about 30% of the bit-rate is saved with the use of SBR. However, the improved performance contributed by SBR results in a huge increase of computational complexity. With more and more multimedia application focus on the portable devices or low-cost media processors, the demand for low-power design becomes an important issue so that the high computational complexity of HE-AAC is undesirable.
In this thesis, we implement an HE-AAC decoder over the Trimedia DSP chip and employ several algorithms to improve the performance. Besides, a power evaluation tool is also used to testify that the algorithms adopted do decrease the power dissipation of the decoder.
According to the profiling analysis, Quadrature Mirror Filters (QMF) used in SBR takes about 70%-80% execution time on HE-AAC decoder. To reduce the complexity of QMF, a real-valued filterbank (LP-SBR) is first applied. We further accelerate the QMF process via filterbank decomposition methods. Besides, 16-bit fixed-point representation of QMF samples are applied not only to increase the performance by faster operations but also to make it possible utilizing the inherent parallelism characteristics of Trimedia DSPs. With Trimedia Very Long Instruction Word (VLIW) architecture and Single Instruction Multiple Data (SIMD) instruction set, every two QMF samples can be operate in a single instruction to accelerate the QMF process. Though the quality loss caused by LP-SBR and fixed-point approximation is nearly imperceptible, a quality enhancement method is applied to compensate the quality degradation. With the proposed schemes, the HE-AAC decoder achieves high coding performance with still high sound quality.
Subjects
音訊解碼器
HE-AAC
SBR
AAC
QMF
Trimedia
VLIW
SIMD
Type
thesis