Speech Bandwidth Extension: Extrapolations of Spectral Envelop and Harmonicity Quality of Excitation

This paper presents a method for restoration of the missing bandwidth of narrowband speech signals. Speech is decomposed into a linear prediction (LP) model of the spectral envelop and a harmonic plus noise model (HNM) of speech excitation. The LP spectral envelope and HNM excitation parameters of the narrowband speech are extrapolated using codebooks trained on narrowband and wideband speech. A novel contribution of this paper is the introduction of a parametric measure of the harmonicity of excitation in harmonically-spaced sub-bands. The wideband LSF parameters and the degree of harmonicity of missing excitation are estimated from those of the narrowband speech via codebook mapping. The method is successful in restoring the harmonicity of speech and converts telephone quality speech to perceptually high quality wideband speech.