High Efficiency Advanced Audio Coding Research Articles

Improved MPEG-4 high-efficiency AAC with variable-length soft-decision decoding of the quantized spectral coefficients

MPEG-4 High-Efficiency Advanced Audio Coding (HE-AAC) is designed for low bit rate applications, such as audio streaming in mobile communications. The HE-AAC audio codec offers a better coding efficiency since variable-length codes (VLCs) are adopted. However, HE-AAC has originally been designed for storage and error-free transmission conditions. For the transmission over bit error-prone channels, error propagation is a serious problem for the VLCs. Therefore, a robust HE-AAC decoder is desired, especially for mobile communications. In contrast to traditional hard-decision decoding, utilizing bit-wise channel reliability information, soft-decision (SD) decoding has been known to offer better audio quality. In HE-AAC, the global gain parameter is coded with fixed-length codes (FLCs), while the scale factors and quantized spectral coefficients are coded with VLCs. In this work, we apply FL/SD decoding to the global gain parameter, VL/SD decoding to the parameters scale factors and quantized spectral coefficients. Especially, in order to apply VL/SD decoding to the quantized spectral coefficients, a new modified trellis representation in VL/SD decoding is proposed. An improved HE-AAC performance is clearly observed, with the support of both instrumental measurements and a subjective listening test.

Autocorrelation Modulation-Based Audio Blind Watermarking Robust Against High Efficiency Advanced Audio Coding

High Efficiency Advanced Audio Coding (HE-AAC) is a lossy compression method for digital audio data which supplies high-quality audio at a very low bit rate. In this paper, the audio blind watermarking algorithm, on the basis of autocorrelation modulation, is introduced to maximize the robustness against low-bit rate HE-AAC. The watermark is embedded by modulating the normalized correlation of the original signal as well as its delayed version. The signal-to-noise ratio of before and after HE-AAC compression decides the strength of the embedding watermark. The watermarking embedding strength is guaranteed by the feedback process. The effectiveness of the proposed method is proven using the Perceptual Evaluation of Audio Quality algorithm and bit error rate of recovered watermarks under HE-AAC compression on mono, stereo and 5.1 channel audio. Experimental results show that the proposed method provides good performance in terms of imperceptibility, robustness and data payload compared with some recent state-of-the-art watermarking methods under an MPEG-2 Audio Layer III (MP3) compression attack.

MPEG Unified Speech and Audio Coding

The MPEG Audio Subgroup has a rich history of accomplishments in creating music coding technology. At higher bit rates, MPEG technology can represent arbitrary sounds, including the human voice, with excellent quality. MPEG-1 and MPEG-2 Audio coders use perceptually shaped quantization noise as the primary tool for achieving compression. The MPEG-4 High-Efficiency Advanced Audio Coding (AAC) standard is a single technology capable of compressing speech, speech mixed with music, or music signals with quality that is always at least as good as the best of two state-of-the-art reference codecs, one optimized for speech and mixed content (AMR-WB B;) and the other optimized for music and general audio (HE-AACv2). This article provides an overview of the USAC architecture and summarizes the performance relative to the best state-of-the-art speech and audio codecs.

Decimation-Whitening Filter in Spectral Band Replication

MPEG-4 High-Efficiency Advanced Audio Coding (HE-AAC) has adopted spectral band replication (SBR) to efficiently compress the high-frequency part of the audio. In SBR, linear prediction is applied to low-frequency subbands to suppress tonal components and smooth the associated spectra for replicating to high-frequency bands. Such a tone-suppressing process is referred to as whitening filtering. In SBR, to avoid the alias artifact incurred by spectral adjustment, a complex filterbank instead of real filterbank is adopted. For QMF subbands, this paper demonstrates that the linear prediction defined in the SBR standard results in a predictive bias. A new whitening filter, called the decimation-whitening filter, is proposed to eliminate the predictive bias and provide advantages in terms of noise-to-signal ratio measure, frequency resolution, energy leakage, and computational complexity for SBR.

MPEG-4 high-efficiency AAC coding [Standards in a Nutshell

The name MPEG-4 high-efficiency AAC (HE-AAC) refers to a family of recent audio coders that was developed by the International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) Moving Picture Experts Group (MPEG) by subsequent extension of the established Advanced Audio Coding (AAC) architecture. These algorithmic extensions facilitate a significant increase in coding efficiency relative to previous standards and other known systems. Thus, they provide a representation for generic audio/music signals that offers high audio quality also to applications limited in transmission bandwidth or storage capacity, such as digital audio broadcasting and wireless music access for cellular phones. This article presents a compact overview of the evolution, technology, and performance of the MPEG-4 HE-AAC coding family.

Fast decomposition of filterbanks for the state-of-the-art audio coding

This letter derives fast decomposition for the quadrature mirror filterbanks (QMFs) of the low power spectral band replication (SBR) tools in the MPEG high efficiency advanced audio coding (HE AAC) decoder. In contrast with the standard method where computation-intensive matrix operations are employed in the QMF, the proposed method decomposes the matrix operations into conventional discrete cosine transform of type II and III (DCT-II and DCT-III) and simple permutations for easy implementation. The computational complexity can be also reduced effectively by using fast algorithms for DCT.