Adaptive postfiltering for quality enhancement of AVS-M coded music

An adaptive post filtering algorithm for enhancing the quality of coded music is presented for the AVS-M decoder. The post filter consists of a long-term post filter in cascade with a short-term post filter section and includes spectral tilt compensation and automatic gain control. The long-term module emphasizes periodic harmonics and attenuates the spectral valleys between periodic harmonics. We use the autocorrelations to indicate the degree of the harmonics and only when the harmonic degree beyond a given threshold the long-term module will be adopted. The short-term module, on the other hand, emphasizes music formats and attenuates the spectral valleys between formats. Unlike earlier post filters which generally introduced a substantial amount of muffing to the output audio signal, our post filter significantly reduces this effect by minimizing the spectral tilt in its frequency response. As a result, this post filter achieves noticeable noise reduction while introducing only minimal distortion in the output music of AVS-M.