An implementation of filterbank for MPEG-2 AAC on FPGA

MPEG-2 AAC is the widely used audio standard and getting more popular for commercial use. In the AAC, the filterbank tool, which is composed of IMDCT, windowing and overlap-add, has the highest computation complexity. In this three steps, IMDCT is the important component. Hence, most published filterbank algorithms focus mainly on the implementation of IMDCT but overlook the relevancy between the steps. This paper proposed a novel architecture of filterbank tool and its hardware implementation. A fast algorithm for IMDCT which contains pre-IFFT, N/4-point IFFT and post-IFFT is employed. In order to improve the efficiency of memory access, windowing and overlap-add operation are combined with post-IFFT, which means no storage elements are required between them and results of post-IFFT will perform windowing and overlap-adding directly. This proposed architecture contains three hardware modules and further improvements are made to each module as well. Totally, 4 multipliers are shared by them in different time. Each module reads data continually from RAM, just like pipeline operation. As a result, this new architecture can improve the memory access efficiency with a speedup of 75% in computation time over the unoptimized one.