Design and Implementation of AAC audio coder

• Main Authors: Hsing-Yang Huang, 黃興洋
• Other Authors: Mong-Kai Ku
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/58945082713462878185

碩士 === 國立臺灣大學 === 資訊工程學研究所 === 92 === AAC provides the highest compression rate and quality among all audio coding standards. However, the complexity of AAC encoder is also very high. The high complexity mainly comes from the great amount of operations performed in filter bank, psychoacoustic model, and bit allocation module. In this thesis, we study fast algorithms and try to reduce the complexities of filter bank and bit allocation module. The fast MDCT algorithm takes advantage of the relationship between MDCT and O2DFT (Odd Time Odd Frequency DFT), reduces the MDCT computation to N/4 points FFT. As for bit allocation module, we apply fast initial gain search method and noise estimation method to develop a new bit allocation module. New bit allocation module reduces the two nested loop structure to one single loop. The complexity is much lower comparing to the bit allocation module proposed in AAC standard. These algorithms efficiently reduce the complexities of filter bank and bit allocation module. Comparing to the famous coder FAAC, our coder saves 50% encoding time and still maintains good quality.