Synchronous overlap and add of spectra for enhancement of excitation in artificial bandwidth extension of speech

In this paper, a new approach that extends narrow-band excitation signals using synchronous overlap and add (SOLA) of spectra have been proposed. Although artificial bandwidth extension (ABE) of speech has been extensively studied, the role of excitation spectra has not been as widely studied as the spectral envelope extension. In this study ABE is investigated with the widely used source-filter framework, where speech signal is decomposed into excitation signal (source) and spectral envelope (filter). For the spectral envelope extension, our former work based on hidden Markov model has been used. For the excitation signal extension, we propose a SOLA of excitation spectra, where the high end of the excitation spectra is extended by preserving the harmonic structure. In experimental studies, we also apply two other well-known extension techniques for excitation signals. Then comparatively we evaluate the overall performance of proposed system using the PESQ metric. Our findings indicate that the proposed excitation extension method delivers significant quality improvements.