A New Post-Filtering for Artificially Replicated High-Band in Speech Coders

Pure estimation in bandwidth extension of bandlimited speech does not provide transparent quality in the extended band. Combining coding and estimation of the missing band can achieve higher quality by transmitting additional information. However, substantial artifacts can remain in the extended band. In this paper, we introduce a new postfiltering designed to reduce these artifacts. Based on a source-filter model, the adopted bandwidth extension transmits spectral envelope parameters, while estimates the excitation at the receiver. The perceptual quality is then enhanced by processing the estimated excitation by a short-term and a long-term postfilter. Objective and subjective assessments show substantial gains when using the new postfiltering. It confirms that low bit-rate wideband coding based on bandwidth extension can get closer to the performances of the single band wideband coders