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.

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