Normalized amplitude quotient for parametrization of the glottal flow

TLDR

The study introduces the normalized amplitude quotient (NAQ) as a method to parametrize the glottal closing phase using two amplitude‑domain measurements derived from inverse‑filtered waveforms. NAQ is calculated by taking the ratio of the acoustic flow amplitude to the negative peak of the flow derivative, then normalizing this ratio by the fundamental period length. NAQ outperforms the conventional closing quotient in robustness to noise and effectively distinguishes breathy, normal, and pressed vowels.

Abstract

Normalized amplitude quotient (NAQ) is presented as a method to parametrize the glottal closing phase using two amplitude-domain measurements from waveforms estimated by inverse filtering. In this technique, the ratio between the amplitude of the ac flow and the negative peak amplitude of the flow derivative is first computed using the concept of equivalent rectangular pulse, a hypothetical signal located at the instant of the main excitation of the vocal tract. This ratio is then normalized with respect to the length of the fundamental period. Comparison between NAQ and its counterpart among the conventional time-domain parameters, the closing quotient, shows that the proposed parameter is more robust against distortion such as measurement noise that make the extraction of conventional time-based parameters of the glottal flow problematic. Experiments with breathy, normal, and pressed vowels indicate that NAQ is also able to separate the type of phonation effectively.