Compressible flow simulations of voiced speech using rigid vocal tract geometries acquired by MRI.

Voiced speech consists mainly of the source signal that is frequency weighted by the acoustic filtering of the upper airways and vortex-induced sound through perturbation in the flow field. This study investigates the flow instabilities leading to vortex shedding and the importance of coherent structures in the supraglottal region downstream of the vocal folds for the far-field sound signal. Large eddy simulations of the compressible airflow through the glottal constriction are performed in realistic geometries obtained from three-dimensional magnetic resonance imaging data. Intermittent flow separation through the glottis is shown to introduce unsteady surface pressure through impingement of vortices. Additionally, dominant flow instabilities develop in the shear layer associated with the glottal jet. The aerodynamic perturbations in the near field and the acoustic signal in the far field are examined by means of spatial and temporal Fourier analysis. Furthermore, the acoustic sources due to the unsteady supraglottal flow are identified with the aid of surface spectra, and critical regions of amplification of the dominant frequencies of the investigated vowel geometries are identified.

Skewing of the glottal flow with respect to the glottal area measured in natural production of vowels.

In the production of voiced speech, glottal flow skewing refers to the tilting of the glottal flow pulses to the right, often characterized as a delay of the peak, compared to the glottal area. In the past four decades, several studies have addressed this phenomenon using modeling of voice production with analog circuits and computer simulations. However, previous studies measuring flow skewing in natural production of speech are sparse and they contain little quantitative data about the degree of skewing between flow and area. In the current study, flow skewing was measured from the natural production of 40 vowel utterances produced by 10 speakers. Glottal flow was measured from speech using glottal inverse filtering and glottal area was captured with high-speed videoendoscopy. The estimated glottal flow and area waveforms were parameterized with four robust parameters that measure pulse skewness quantitatively. Statistical tests obtained for all four parameters showed that the flow pulse was significantly more skewed to the right than the area pulse. Hence, this study corroborates the existence of flow skewing using measurements from natural speech production. In addition, the study yields quantitative data about pulse skewness in simultaneous measured glottal flow and area in natural production of speech.

Vowel formants from the wave equation.

This article describes modal analysis of acoustic waves in the human vocal tract while the subject is pronouncing [o]. The model used is the wave equation in three dimensions, together with physically relevant boundary conditions. The geometry is reconstructed from anatomical MRI data obtained by other researchers. The computations are carried out using the finite element method. The model is validated by comparing the computed modes with measured data.