A low cost adaptive transform decoder implementation for high-quality audio

Low-cost, 16-b fixed-point digital signal processing (DSP) chips have traditionally been used in real-time wideband audio implementations due to limited arithmetic precision, which can lead to audible roundoff errors. The authors describe a real-time AC-2 stereo digital audio decoder implementation based on one 16-b TMS320C5x DSP. This is achieved by modifying a conventional inverse fast Fourier transform (FFT) computation, using a form of mixed-precision arithmetic, and exploiting the short instruction cycle time of the DSP. Compared with a 16-b single-precision implementation, a moderate increase in required DSP cycle time is incurred. The results indicate that the dynamic range of the 16-b DSP decoder is currently within 1 to 3dB of that obtained by current high-quality 16-b A/D and D/A converters. A further refinement will produce a dynamic range figure which meets or exceeds that obtained by higher-precision fixed-point ALUs