Postfiltering for Suppression of Residual Echo from Vocoder Distortion in Packet-Based Telephony

This paper investigates postfiltering for residual echo suppression in networks employing low-bit-rate speech compression in the echo path. Simulations show that the residual echo from nonlinear vocoder distortion with ITU G.729 is proportional to the input signal LPC spectrum. An algorithm is proposed to estimate the residual echo power spectrum using a frequency-dependent scaling factor. The algorithm is incorporated into a psychoacoustic postfilter for residual echo suppression and compared to an existing estimator with a fixed scaling factor. Experiments with speech input and near-end signals show an average 0.85 dB lower spectral distortion and 0.4 higher estimated mean opinion score