Vocal folds vibratory patterns of “laryngeal mechanism M0” as investigated with high-speed cinematography and electroglottography

International audienceA human vocal production is characterized by the use of different laryngeal mechanisms<br />(Roubeau,1993 ; Henrich et al., 2003), among which laryngeal mechanisms M1 and M2 are<br />the most frequently used and studied in speech and singing. Chest, or modal voice, is<br />produced in M1, while falsetto, or female head voice is produced in M2. Besides that, another<br />mechanism known as laryngeal mechanism 0 (M0) can also be found in speech and some<br />types of singing. Vocal fry, pulse register, creaky voice, glottal fry are the terms frequently<br />used to refer to this vocal production. Yet, these terms are sometimes considered as<br />synonymous (Hollien, 1974), while in other cases, they would characterize different vocal<br />productions. The M0 mechanism has mainly been studied for pathological voices, but it is<br />also of interest for linguists, as it can be found in hesitations and at the end of utterances.<br />Thus our aim is to investigate the different vibratory patterns that can be involved in M0<br />thanks to high speed cinematography and to compare them with the EGG signal. The glottal<br />vibratory movement has been simultaneously investigated in two ways: first, with the help of<br />electroglottography (EGG), and secondly, with high-speed cinematography. The high-speed<br />images have been recorded using a high-speed camera unit Wolf HS Endocom 5560, and the<br />EGG signal has been recorded using a Laryngograph Ltd. Two male speakers were asked to<br />produce a sustained vowel in M0 with or without vocal effort, and transitions between M1<br />and M0. The high-speed images and the EGG signal were recorded simultaneously at<br />different sampling frequencies, respectively 4000 Hz and 44170 Hz. The data were then<br />processed using Matlab. The EGG signal was differentiated, and both EGG and Differentiated<br />EGG (DEGG) signals were synchronized with the high-speed images, so as to compare the<br />EGG and DEGG data with the vibratory movements observed on the images. An image<br />processing algorithm based on the detection of contrast (light energy threshold) was<br />developed for relative measurement of glottal area, antero-posterior and transversal distances.<br />It is a known fact that the glottal area function in M0 is characterized by short pulses, which<br />can be single, double or triple within a fundamental period (Whitehead et al., 1984 ; Childers<br />and Lee, 1991).<br />On a physiological point of view, the thyroarytenoid muscles tend to shorten, subsequently<br />thickening the anterior-posterior dimension of the vocal folds, and allowing the anterior part<br />of the vocal ligaments to vibrate (Hollien, 1974). However the physiological properties<br />associated with the multiple vibratory patterns mentioned above are not fully described,<br />especially regarding the precise movements of the vocal folds margins, the degree of vocal<br />fold adduction and the contribution of the ventricular folds.<br />The analysis shows that different realizations of M0 can be found in this corpus especially<br />when comparing (i) the M0 realized with vocal effort from (ii) the M0 realized without vocal<br />effort. The first one is more likely to be characterized by a single pulse, while the second one<br />is frequently produced with multiple pulses - both realizations having different typical EGG<br />shapes. We also found that in the case of single pulse pattern, the anterior portion of the vocal<br />folds is more involved in the vibrating process than the posterior one, while the posterior<br />portion of the vocal folds can also be active in the case of a multiple pulse pattern. Transitions<br />produced by the two speakers were also investigated, thus revealing different which were<br />possibly used. The validity of EGG signals rendering the different vibratory patterns will be<br />discussed as well as implications for synthesis