Minimal Word-width Implementation of Dolby Ac-3 and Iso Mpeg Audio Decompression Standards

Digital Audio Broadcasting (DAB) is an emerging technology which is currently experiencing rapid growth following the advent of ETS 300-401 DAB standard in Europe and the ATSC ATV standard in the U.S. Wide-band audio compression is performed by ISO-MPEG layer II for DAB, and by Dolby AC-3 for ATV. To achieve high quality audio, current DSP implementations for such compression algorithms typically use word-widths in excess of 18 bits. Implementation on industry standard 16-bit DSP devices has to date required double-precision arithmetic. By suitable formulation of the synthesis transformation to allow dynamic scaling, high quality audio using single precision arithmetic can be achieved on a 16-bit data path. To illustrate this approach, an implementation of Dolby AC-3 utilising this technique is described. An alternative is also described: a mixed single-and-double precision direct implementation which exploits the variable precision requirements within the synthesis transform algorithm, thus yielding a low complexity solution.