Noise post processing based on a stationary noise generator

The paper presents a newly developed noise post-processing (NPP) algorithm for improving subjective performance of low bit-rate code excited linear prediction (CELP) decoding. The algorithm is based on a stationary noise generator and improves subjective quality of a noisy signal input. A backward adaptive detector defines noisy input signal segments from decoded line spectral frequency (LSF), energy, and pitch parameters. By using LSF and energy parameters from the past, the noise generator estimates and produces stationary noise. The algorithm is independent of the main codec algorithm and is applicable to any CELP decoder. When applied to G.729 and G.723.1, our test results show that the algorithm improves subjective performance at around 0.2-0.8 in degradation category rating (DCR) mean opinion score (DMOS) under several background noise conditions.