A flow waveform-matched low-dimensional glottal model based on physical knowledge

Abstract

The purpose of this study is to explore the possibility for physically based mathematical models of the voice source to accurately reproduce inverse filtered glottal volume-velocity waveforms. A low-dimensional, self-oscillating model of the glottal source with waveform-matching properties is proposed. The model relies on a lumped mechano-aerodynamic scheme loosely inspired by the one- and multimass lumped models. The vocal folds are represented by a single mechanical resonator and a propagation line which takes into account the vertical phase differences. The vocal-fold displacement is coupled to the glottal flow by means of an aerodynamic driving block which includes a general parametric nonlinear component. The principal characteristics of the flow-induced oscillations are retained, and the overall model is able to match inverse-filtered glottal flow signals. The method offers in principle the possibility of performing transformations of the glottal flow by acting on the physiologically based parameters of the model. This is a desirable property, e.g., for speech synthesis applications. The model was tested on a data set which included inverse-filtered glottal flow waveforms of different characteristics. The results demonstrate the possibility of reproducing natural speech waveforms with high accuracy, and of controlling important characteristics of the synthesis such as pitch.

A One-Mass Physical Model of the Vocal Folds with Seesaw-Like Oscillations

“…A mass-spring system is also attached to the glottis at its entrance to make it oscillate with the displacement of the mass. This work is similar to those proposed in (Liljencrants, 1991;Avanzini et al, 2001;Drioli, 2002). In the present work, the introduction of the fulcrum point position is responsible for the control over the amplitude and the shape of the glottal flow.…”

“…The glottal model presented here is a simplified version of the body-cover model in line with the model proposed in (Drioli, 2002). In the present model the propagation of mucosal wave is highly approximated by the seesaw-like rotary motion about its fulcrum point P 0 (X 0 , Y 0 ) adjustable in both the horizontal and vertical directions.…”

“…In the proposed model the glottal exit displacement is expressed by the glottal entry displacement with phase difference of 180 degrees due to the oscillation of the seesaw-like glottis about its fulcrum point. We compare our results with the surface wave propagation method mentioned in (Titze, 1988;Drioli, 2002). In this approach the glottal exit displacement is represented by…”

“…For simplicity we assume in all simulations that X 01 = X 02 and keep the sub-glottal pressure constant at P s = 300 Pa (3.059 cm H 2 O). This constant value of the sub-glottal pressure falls in the range considered in (Drioli, 2002). First of all we present the simulation of the model for the case when the vertical position of the fulcrum point is in the middle of the glottis, i.e.…”

“…In view of this observation, the motion of a vocal fold may be regarded as the propagation of a surface wave along the bodycover from the bottom to the top of the glottis. Body-cover models based on this hypothesis were presented in (Titze, 1988;Story, Titze, 1995;Drioli, 2002).…”