Evaluation of cepstral lifters for articulatory codebook search

Abstract

Of great importance for the success of the articulatory approach to speech coding [Schroeter et al., IEEE‐ICASSP, 308–311 (1987)] is the use of a good distance measure between a given speech signal and the entries in a stored codebook of impulse responses and corresponding vocal tract shapes (articulatory codebook). One promising distance measure is the weighted cepstral distance. Since the impulse responses in the articulatory codebook do not include glottal characteristics, optimal weighting functions (cepstral lifters) are derived to reduce the influence of a varying glottal source on the cepstral distance measure. This is done by examining the ensemble of cepstral coefficients of speech produced by an articulatory speech synthesizer that also includes a vocal‐cord model. The obtained cepstral lifters are optimal for the given ensemble of cepstral coefficients and for given constraints on the weighting function. They are different for cepstral coefficients derived from the power spectrum (FFT cepstra) and those derived from LPC coefficients (LPC cepstra). The performances of the obtained cepstral lifters are compared in an articulatory codebook search.