Coding bit rate scalability of MPEG audio data

Users previously had to use transcoding methods in which a coded audio stream was decoded and the decoded audio then reencoded at the desired bit rate. Data processing of coded audio therefore usually involves complex and time-consuming tasks. In this paper, we describe three algorithms for bit rate scaling on coded MPEG data domains. One is a bandwidth limitation method to 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 obtained in the bitstream in order to improve bit rate scaling efficiency. The simulation results show that the requantization process provides very high conversion efficiency and that sound quality nearly equal to that of direct coding can be obtained by utilizing the psychoacoustic model. It was also shown that very fast scaling (factor of six) can be achieved compared with the conventional baseband transcoding method. © 2001 Scripta Technica, Electron Comm Jpn Pt 3, 84(10): 47–56, 2001