Finite element modeling of the effects of velopharyngeal opening on vocal tract reactance in female voice.

Classical singers use nasal consonants as "resonance exercises," and experimental results have shown that singers may use some velopharyngeal opening (VPO), most often in [a:] and more seldom in [i:] or [u:]. In particular, male singers have been found to increase VPO as pitch rises toward register change frequencies (passaggi). Laryngoscopic findings have shown that some VPO stabilizes vocal fold vibration; the effect is related to positive reactance. This study investigates the effects of VPO on vocal tract (VT) reactance over the range of fundamental frequencies (f0) used in singing using a computerized tomography-based finite element model of the VT and nose of a female. According to the results, by raising the lowest VT resonances, the VPO increased the VT reactance in the frequency ranges 207-359 Hz for [i:], 265-411 Hz for [u:], and 500-611 Hz for [a:], depending on the VPO size (full or half VPO). These frequency ranges are close to the first and second passaggio of a female singer. The change may have an especially practical stabilizing effect for [a:], which is otherwise characterized by very large changes in VT reactance and negative reactance at the second passaggio.

Influence of nasal cavities on voice quality: Computer simulations and experiments.

Nasal cavities are known to introduce antiresonances (dips) in the sound spectrum reducing the acoustic power of the voice. In this study, a three-dimensional (3D) finite element (FE) model of the vocal tract (VT) of one female subject was created for vowels [a:] and [i:] without and with a detailed model of nasal cavities based on CT (Computer Tomography) images. The 3D FE models were then used for analyzing the resonances, antiresonances and the acoustic pressure response spectra of the VT. The computed results were compared with the measurements of a VT model for the vowel [a:], obtained from the FE model by 3D printing. The nasality affects mainly the lowest formant frequency and decreases its peak level. The results confirm the main effect of nasalization, i.e., that sound pressure level decreases in the frequency region of the formants F1-F2 and emphasizes the frequency region of the formants F3-F5 around the singer's formant cluster. Additionally, many internal local resonances in the nasal and paranasal cavities were found in the 3D FE model. Their effect on the acoustic output was found to be minimal, but accelerometer measurements on the walls of the 3D-printed model suggested they could contribute to structure vibrations.

The Human Vocal Fold Layers. Their Delineation Inside Vocal Fold as a Background to Create 3D Digital and Synthetic Glottal Model.

OBJECTIVES: To distinguish the layers of the vocal fold at the submacroscopic level and determine their boundaries, thereby creating a basis for the construction of a digital 3D model of the human vocal folds. STUDY DESIGN: The submacroscopic delineation of individual layers of fixed vocal ligaments based on their structural differences. METHODS: Following tasks were performed: (1) Submicroscopic dissection of the vocal folds fixed in a solution with a low concentration of fixation substance (in this case, the muscular parts of the vocal folds were removed); (2) Using the CT and micro-MRI methods, we determined the position of the dense parts of the vocal folds; and (3) Using a modified plastination method, we preserved macroscopically natural appearance of all ligamentous and muscular layers. RESULTS: The vocal ligament is composed of several volumes of connective tissue. It is surrounded by layers of fibrous material permeated by liquid. Individual fibers stretch all the way to the fibrous casing (fascia) of the vocal muscle. The vocal fold layer surrounding the ligament externally has a stratified character. CONCLUSIONS: According to our findings, we infer that this ligament is a complex of several fibrous bundles which are surrounded by a thin layer of connective tissue. Below the surface of epithelium of the vocal fold run several separate bands which are closely adjacent to it. Therefore, we propose using the term ligamentous complex involving closely adjacent structures, instead of the vocal ligament only. We feel that it better reflects the functional and structural character of the whole formation.

Human vocal tract resonances and the corresponding mode shapes investigated by three-dimensional finite-element modelling based on CT measurement.

Resonance frequencies of the vocal tract have traditionally been modelled using one-dimensional models. These cannot accurately represent the events in the frequency region of the formant cluster around 2.5-4.5 kHz, however. Here, the vocal tract resonance frequencies and their mode shapes are studied using a three-dimensional finite element model obtained from computed tomography measurements of a subject phonating on vowel [a:]. Instead of the traditional five, up to eight resonance frequencies of the vocal tract were found below the prominent antiresonance around 4.7 kHz. The three extra resonances were found to correspond to modes which were axially asymmetric and involved the piriform sinuses, valleculae, and transverse vibrations in the oral cavity. The results therefore suggest that the phenomenon of speaker's and singer's formant clustering may be more complex than originally thought.

Vocal tract changes caused by phonation into a tube: a case study using computer tomography and finite-element modeling.

Phonation into a glass tube is a voice training and therapy method that leads to beneficial effects in voice production. It has not been known, however, what changes occur in the vocal tract during and after the phonation into a tube. This pilot study examined the vocal tract shape in a female subject before, during, and after phonation into a tube using computer tomography (CT). Three-dimensional finite-element models (FEMs) of the vocal tract were derived from the CT images and used to study changes in vocal tract input impedance. When phonating on vowel [a:] the data showed tightened velopharyngeal closure and enlarged cross-sectional areas of the oropharyngeal and oral cavities during and after the tube-phonation. FEM calculations revealed an increased input inertance of the vocal tract and an increased acoustic energy radiated out of the vocal tract after the tube-phonation. The results indicate that the phonation into a tube causes changes in the vocal tract which remain also when the tube is removed. These effects may help improving voice production in patients and voice professionals.