Memory Reduction Technique of Spreading Function in MPEG AAC Encoder

Shih-Way Huang; Liang-Gee Chen; Tsung-Han Tsai
DAFx-2004 - Naples
In order to reduce the computational complexity of an MPEG AAC encoder, calculation of spreading function, which is the critical algorithm in the psychoacoustic model, can be replaced with look-up tables. However, the memory size of the table is considerably large in DSP or hardware implementation for portable devices. The paper deals with the methods to reduce the memory size. We modified a method originally used in an MP3 software encoder and adopted it in an MPEG AAC encoder. The result shows that only about one-third of the original size is required in programmable processor implementation such as DSP. Moreover, for hardware implementation, we analyzed the wordlength and reduced the size to only 3.6% compared to that for a 16-bit DSP while maintaining audio quality.