Effects of glottal and velopharyngeal port openings on the first formant frequency in natural speech

The present study investigated the effects of the glottal opening during phonation and small openings of the velopharyngeal port on the first vowel formant frequency (F1). While previous studies confirmed that these boundary conditions increase the formant frequencies of speech sounds based on models and simulations, such a trend was so far not evident in in vivo experiments with humans. To estimate the effects of the boundary conditions on F1 in natural speech, we recorded the audio signal simultaneously with optopalatography (OPG), electroglottography, and nasal airflow of 21 speakers producing logatomes with the eight German tense vowels under varying conditions. The effects of oral articulation were controlled using OPG and larynx height measurements. An increase in average glottal area, approximated based on glottal open quotient, tended to decrease F1. This finding contradicts the predictions from previous simulation studies regarding the glottal boundary condition. On the other hand, a small increase in the estimated area of the velopharyngeal port opening increased F1 in both spoken and shouted vowels. These results provide evidence that F1 is not only determined by the cross-sectional area function of the vocal tract, but is also affected by small openings of the velopharyngeal port.