Optimized group delay based estimation of glottal closure instants

Sophisticated voice source estimation techniques, such as closed-phase pitch synchronous inverse filtering method, relay on accurate estimates of glottal closure instants (GCIs). In this paper, a group delay approach to GCI estimation is presented. Specifically, the average group delay and the energy weighted group delay measures are discussed in detail. We propose an improvement to the implementation of the group delay measures, whereby translation invariant thresholding is used to remove aspiration noise and other disturbances from the LPC residue instead of the standard 2^nd order Butterworth low-pass filter. The performances of the two group delay measures with and without the proposed improvement are evaluated for a range of fixed and pitch-synchronous group delay window lengths. The results show that the optimal GCI estimation performance is achieved with the energy weighted group delay measure, translation invariant thresholding of LPC and the window length equaling exactly one pitch period.