An Improved Algorithm for AAC Window Determination and Quantization

In order to achieve a better coding performance, Advanced Audio Coding (AAC) uses the complex psychoacoustic model and the two nested-loop quantization, but the high-level complexity of the above algorithms will badly affect the real-time encoding, so it is necessary for the real-time encoding system to improve the algorithm for AAC window determination and quantization. For the window determination in AAC psychoacoustics model, this paper proposes a new window determination method which is based on the variance ramp in time-domain, on the other hand, in the quantization of this paper, no loop is required for the variable bit rate condition and only single loop is required for the constants bit rate condition, the quantization algorithms is realized by the deriving of the accurate model of quantization noise and the defining of the initial scale-factor in the quantization. Moreover, for the constants bit rate condition, the number of quantization iterations at 96kbps bit rate is only about 1-2. In the last examination, the test results showed that our window determination algorithms requires only 1.79 MCPS and our quantization algorithms needs only 14.67 MCPS in TMS320C6727B platform , while the encoding audio quality have almost no impairment.