This paper proposes optimization techniques to implement MPEG audio decoding algorithms in real-time using general-purpose 32-bit MCU RISC processor. Both MP3 and AAC LC profile decoding algorithms can be partitioned into two parts: control-intensive part and computation-intensive part. Optimization techniques in this study are focused on developing methodologies that are suitable for each part. We implemented MP3/AAC decoder using ARM-based RISC MPU and its test board. Both designed decoders with proposed optimizations could achieve decoding processes in real-time within an operating frequency of 35 MHz. ISO 13818-4 compliance test results confirmed that the proposed decoders ensured full compliance with the ISO 13818-3 audio decoder. These implementation results illustrate the efficiency of the proposed design methodology in both performance and cost.