In this paper low power techniques for MP3 audio decoder are used based on a phenomenon of zero-filled subbands. By our analysis, large part of subbands contains useless zero-valued data, which can be cut-off. We propose an effective architecture to gain incremental improvements in power consumption and computation complexity. In DWIMDCT block, the computational complexity can be reduced to 34% when we combine the subband cut-off technique and our proposed fast algorithm. In SIMDCT block of Synthesis filterbank, the same technique can be applied and the computational complexity can be reduced to 17%. This subband cut-off approach is simple and can be easily integrated with other designs.