MPEG audio bit rate scaling on coded data domain

Formerly, once the audio data is compressed, transcoding is used to scale the bit rate, where decoding and re-encoding are taken place. Therefore, data manipulation of coded data has been very complex and time consuming work. In this paper, we describe three algorithms for bit rate scaling on coded MPEG data domain. One is bandwidth limitation method cutting higher frequency components until target data rate is satisfied. The other two use re-quantization process where a quantization step in each subband is modified. One of them reflects psychoacoustic model from bit allocation information obtained in the bitstream in order to improve bit rate scaling efficiency. The simulation results show that re-quantization process provides very high conversion efficiency and nearly equal sound quality to direct coding one can be obtained by retlecting psychoacoustic model. It is also shown that very fast scaling(factor of six) have been achieved when compared with transcoding method.