The Implementation And Optimization Of MPEG-4 AAC Decoder Based On NIOS II

AAC (Advanced Audio Coding), as the kernel of MEPG-4 audio standard, can encode and decode high quality under 64kbps. It support over 48 audio channels,16 low frequency channels, 16 multi-dub and multi-language channels, and 16 data streams. So it plays a key role in many fields. The NIOS II embedded processor of Altera Co is a kind of processors that can be configured by customer. It has unique advantage in development of audio and video system.In this dissertation, author firstly the algorithms of MPEG-4 audio standard, including the departments of AAC, which are made of noiseless decoding, inverse quantity, applying scale factor, joint stereo decoding, temporal noise shaping, long term prediction, inverse filter bank. Then we introduce the hardware system of NIOS II. Combination with the characteristic of the development system, thirdly, we introduce corrective the optimization technique, including the algorithms of Huffman decode and IMDCT, non-linear operation method in fixed point computation, custom instruction method which is provided by NIOS II, and the realization of MPEG-4 AAC real-time decoder finally.At last, we give the realized results, analyze and technique target of the decoder algorithms on the NIOS II., including the audio objective evaluation. The experiments show that the decoder can realize the real-time decoder at the fast system frequency and there no difference between decoded signal and original subjectively, and similar with MOS objectively.