In MP3/AAC encoders, the quantization parameter called scalefactor controls the quantization noise and the bitrate. Tuning these encoders would require a characterization of the rate-distortion function per subband, which seems to be available only in a parametric manner. In this paper, a fast bit allocation method for MP3/AAC encoder is presented. The resulting encoder is able to produce an ISO/MPEG compliant bitstream which can guarantee better audio quality. More importantly, the number of computational steps is greatly reduced as compared to the method recommended by the ISO/MPEG committee because the efficient bit allocation algorithm significantly reduces the number of iterations required. It was found that the efficient bit allocation algorithm works best when the bit rate demanded by the psychoacoustic model in order to keep the quantization noise below the masking threshold is almost equal to the operational bit rate.
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