Coding bit rate scalability of MPEG audio data

Users previously had to use transcoding methods in which a coded audio stre am was decoded and the decoded audio then reencoded at the desired bit rate . Data processing of coded audio therefore usually involves complex and tim e-consuming tasks. In this paper, we describe three algorithms for bit rate scaling on coded MPEG data domains. One is a bandwidth limitation method t o cut higher frequency components until the target data rate is satisfied. A second method uses a requantization process where a quantization step in each subband is modified, and a third method also utilizes a requantization process with a psychoacoustic model from bit allocation information obtain ed in the bitstream in order to improve bit rate scaling efficiency. The si mulation results show that the requantization process provides very high co nversion efficiency and that sound quality nearly equal to that of direct c oding can be obtained by utilizing the psychoacoustic model. It was also sh own that very fast scaling (factor of six) can be achieved compared with th e conventional baseband transcoding method. (C) 2001 Scripta Technica.