Fast Algorithms for Low-Delay TDAC Filterbanks in MPEG-4 AAC-ELD

Abstract

Abstract-The MPEG committee has completed development of a new audio coding standard called "MPEG-4 advanced audio coding-enhanced low delay" (AAC-ELD). AAC-ELD uses low delay spectral band replication (LD-SBR) technology together with a low delay time domain alias cancellation (LD TDAC) filterbank in the encoder to achieve both high coding efficiency and low algorithmic delay. In this paper, we present fast algorithms for implementing LD-TDAC filterbanks in AAC-ELD. Two types of fast algorithms are presented. In the first, we map LD-TDAC analysis and synthesis filterbanks to modified discrete cosine transform (MDCT) and inverse modified discrete cosine transform (IMDCT), respectively. Since MDCT/IMDCT are already extensively used in AAC and they have many fast algorithms, this mapping not only provides a fast implementation but also allows a common implementation of the filterbanks in AAC Low Complexity (AAC-LC), AAC Low Delay (AAC-LD) and AAC-ELD codecs. In the second algorithm, we provide a mapping to discrete Cosine transform of type II. The mapping to DCT-II allows the merger of the matrix operations with the windowing stage that precedes or follows them. This further reduces the number of multiplications and leads to an algorithm with the lowest known arithmetic complexity. For filterbanks of lengths 1024 and 960, we also present a new fast factorization of 15-point DCT-II that requires only 14 irrational multiplications, 3 dyadic rational multiplications and 67 additions.

International Journal of Electronics and Telecommunications

“…Rongshan Yu,Susanto Rahardja,Lin Xiao,Chi Chung Ko, [7] describes an algorithm called an Advanced Audio Zip. Hence, it produces a lossless audio coding .It provides a better CR.In [5] proposed a method known as LD TDAC analysis (Low delay time domain aliasing cancellation) and faster implementation mapped in synthesis filter bank.These are designed by Codec methods.…”

Reviews on Technology and Standard of Spatial Audio Coding

“…Most of MPEG standard have relatively longer delay than required in a standard two way communication system. Thus, some approaches have been proposed for low delay audio codec such as in [118][119]. It is also interesting to look at approaches based on speech coding, such as in [110][111][112][113][114][115][116][117][118][119][120][121][122][123][124][125], to extend their capability to have full audio band and multichannel speech codec.…”