Waveform extraction for perfect reconstruction in WI coding
Vesa T. Ruoppila, M. Tammi, Jukka P. P. Saarinen · 2002
A signal model used in waveform interpolation (WI) coding assumes implicitly that the pitch period remains constant within a waveform to be extracted. This assumption is utilized for determining waveform boundaries and for forming the discrete Fourier transform (DFT) of the extracted waveform. Therefore, the waveforms do not describe the original signal faithfully during pitch changes even if an accurate pitch estimate is available for each time instant. Due to the distortions occurring in waveform extraction, the original signal cannot be recovered. In this paper, we discuss assumptions of the signal model and present a waveform extraction algorithm which provides asymptotically perfect reconstruction with vanishing quantization error. The algorithm uses cubic B-spline interpolation as the continuous approximation of the signal. The full benefit of the waveform extraction algorithm is obtained when an accurate pitch estimate is available.