Group delay function as a means to assess quality of glottal inverse filtering

The estimation of glottal flow with inverse filtering requires typically subjective evaluation of the obtained flow waveforms by the experimenter. In this paper, we propose a straightforward method that yields an objective analysis tool to be used in the assessment of the quality of inverse filtered glottal flow estimates. The method computes the negative derivative of the phase response, the group delay function, over a single glottal cycle of the estimated flow. Incorrect settings of the anti-resonances of the inverse filter result in distortion of the group delay function. This distortion is easily detectable from the group delay function and can therefore be used in a straightforward manner to analyse how well the zeros of the inverse filter match the poles of the vocal tract.