A 128KB/S HI-FI AUDIO CODEC BASED ON ADAPTIVE TRANSFORM CODING WITH ADAPTIVE BLOCK SIZE MDCT

A hi-fi audio CODEC with an improved adaptive transform coding (ATC) algorithm is developed using digital signal processors (DSP's). An audio signal with a 20 kHz bandwidth sampled at 48 kHz is coded at a rate of 128 kb/s. The algorithm utilizes adaptive block size selection, which is effective for pre-echo suppression. A modified discrete cosine transform (MDCT) with a simple window set is employed to reduce block boundary noise without decreasing the performance of transform coding. In addition, a fast MDCT calculation algorithm, based on a fast Fourier transform, is adopted. Weighted bit allocation is employed to quantize the transformed coefficients. The CODEC is realized by a multiprocessor system composed of newly developed DSP boards. Subjective tests with the CODEC show that the coding quality is comparable to that of compact disc signals.