基于DSP的IMDCT快速算法

One of the Fast DSP-based inverse MDCT algorithm

修正离散余弦变换 ( MDCT)在音视频信号编码中得到广泛地应用 ,其快速算法在实时编解码系统中尤为重要。论文给出了一种适用于数字信号处理器 ( DSP)实现的修正离散余弦反变换 ( IMDCT)快速算法—用 M/ 2点时间抽取 ( decimation in time,DIT)分裂基 FFT实现 2 M点的IMDCT。算法是基于蝶形运算组成 ,在 DSP中可以获得很高的运算效率。该算法的蝶形运算结构同样适用于正向MDCT。在由定点 DSP实现的活动图像专家组 ( MPEG)音频层 III解码器中 ,与 MPEG音频压缩标准 ISO/ IEC 11172 -3中给出的 IMDCT运算量相比较 ,该文提出的 IMDCT快速算法节省了 2 / 3的运算时间和 1/ 2的存储空间。

Modified discrete cosine transform (MDCT) is widely used in audio compression, such as the MPEG audio layer III codec. For the MDCT algorithm on a fixed point digital signal processor (DSP), a butterfly operation of inverse MDCT was proposed to reduce the computational time and memory requirements. The 2 M length inverse MDCT algorithm was derived in the form of a butterfly computation with M /2 points DFT and M points windowing. This fast algorithm operating in ADSP 2181 has at least 66% less instructions and 50% less memory space then the inverse MDCT described in ISO/IEC 11172 3.