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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 and video signal coding, and its fast algorithm is particularly important in real-time codec system. In this paper, we propose a fast modified discrete cosine transform (IMDCT) algorithm suitable for digital signal processor (DSP) implementation - 2 M points with M / 2 decimation in time (DIT) IMDCT. The algorithm is based on butterfly operation, which can achieve high computational efficiency in DSP. The algorithm of butterfly operation is also suitable for forward MDCT. In the Moving Picture Experts Group (MPEG) audio layer III decoder implemented by fixed-point DSP, the IMDCT fast algorithm proposed in this paper saves compared with the IMDCT computation amount given in the MPEG audio compression standard ISO / IEC 11172-3 2/3 of computing time and 1/2 of storage space.