国际标准化组织所建议的标准算法在实现先进音频编码( AAC) 固定码率时，存在码率不稳定和计算量大的问题．为此，文中提出了一种新的固定码率控制算法．该算法在为当前帧分配比特时，充分考虑比特缓冲池的使用情况和编码复杂度，使比特缓冲池真正起到缓冲作用; 同时根据编码所需比特数和感知熵的关系，在量化循环之前进行掩蔽阈值的预调整．实验结果表明，与标准算法相比，文中算法有效减少了量化循环的迭代次数，显著降低了计算复杂度，在不降低音质的情况下获得了更稳定的码率．

In the implementation of constant bitrate in advanced audio coding ( AAC) using the ISO standard algorithm,the bitrate is unstable and the computational complexity is high. In order to solve these problems,a novel constant bitrate control algorithm is proposed. By fully considering the use of the bit buffer and the coding complexity during the allocation of bits for the current frame,the buffer plays its important role. Besides,the mask threshold is pre-adjusted before the quantization loop according to the relationship between the number of bits needed for coding and the perceptual entropy. Experimental results show that,as compared with the standard algorithm,the proposed algorithm effectively reduces the iteration number of the quantization loop,significantly decreases the computational complexity,and produces more stable bitrate without decreasing the audio quality.