Efficient algorithms for MPEG-4 AAC-ELD, AAC-LD and AAC-LC filterbanks

Recently MPEG has developed a new audio coding standard - MPEG-4 AAC enhanced low delay (ELD), targeting low bit rate, full-duplex communication applications such as audio and video conferencing. The AAC-ELD combines low delay SBR filterbank with a low delay core coder filterbank to achieve both high coding efficiency and low algorithmic delay. In this paper, we propose an efficient mapping of the AAC-ELD core coder filterbank to the well known MDCT. This provides a fast algorithm for the new filterbank. Since AAC-LD and AAC-LC profiles also use MDCT filterbank, this mapping enables efficient joint implementation of filterbanks for all 3 profiles. We also present a very efficient 15-point DCT-II algorithm that is useful for implementation of all 3 profiles with frame lengths of 960 and 480. This algorithm requires just 17 multiplications and 67 additions. The overall design structure and complexity analysis of proposed implementation of the filterbanks is also provided.