On Reverse Waterfilling in Closed-Loop LPC with Noise Shaping

A new criterion is derived for the design of the noise weighting filter in linear predictive coding (LPC) that accounts for the issue of noise propagation. It will be shown that the new filter design constitutes an approximation of the reverse waterfilling procedure known from rate-distortion theory and audio transform coding. It improves the overall coding SNR of closed-loop LPC with noise shaping. A practical application within the 3GPP AMRWB codec is presented. Objective test results indicate notable quality improvements.