An amplitude quotient based method to analyze changes in the shape of the glottal pulse in the regulation of vocal intensity

This study presents an approach to visualizing intensity regulation in speech. The method expresses a voice sample in a two-dimensional space using amplitude-domain values extracted from the glottal flow estimated by inverse filtering. The two-dimensional presentation is obtained by expressing a time-domain measure of the glottal pulse, the amplitude quotient (AQ), as a function of the negative peak amplitude of the flow derivative (dpeak). The regulation of vocal intensity was analyzed with the proposed method from voices varying from extremely soft to very loud with a SPL range of approximately 55dB. When vocal intensity was increased, the speech samples first showed a rapidly decreasing trend as expressed on the proposed AQ-dpeak graph. When intensity was further raised, the location of the samples converged toward a horizontal line, the asymptote of a hypothetical hyperbola. This behavior of the AQ-dpeak graph indicates that the intensity regulation strategy changes from laryngeal to respiratory mecha...