The bandwidth-proportional noise-shaping criterion has been proposed to be the optimum bit allocation criterion in the sense of minimizing segmental masking-to-noise ratio [1]. A single loop bit allocation has been developed for ISO/IEC MPEG1layer 3 (MP3) [2] to reduce the complexity over the existing two nested loop method for MP3 encoder. Also, the allocation method also leads to the better compression quality. This paper extends the allocation method to the ISO/IEC MPEG-2/4 Advanced Audio Coding (AAC) [3] [4]. This paper derives the perceptual bandwidth for the scale factor bands, provides the bit consumption trade-off to transmit the bits for the scale factors, and illustrates an efficient sectioning method on the Huffman codebook. All these methods jointly integrate with the bit allocation method to improve the quality and the computing complexity of the widely used AAC reference encoder, FAAC [5].