Finite element generation of sibilants /s/ and /z/ using random distributions of Kirchhoff vortices

Abstract

The numerical simulation of sibilant sounds in three‐dimensional realistic vocal tracts constitutes a challenging problem because it involves a wide range of turbulent flow scales. Rotating eddies generate acoustic waves whose wavelengths are inversely proportional to the flow local Mach number. If that is low, very fine meshes are required to capture the flow dynamics. In standard hybrid computational aeroacoustics (CAA), where the incompressible Navier‐Stokes equations are first solved to get a source term that is secondly input into an acoustic wave equation, this implies resorting to supercomputer facilities. As a consequence, only very short time intervals of the sibilant can be produced, which may be enough for its spectral characterization but insufficient to synthesize, for instance, an audio file from it or a syllable sound. In this work, we propose to substitute the aeroacoustic source term obtained from the computational fluid dynamics (CFD) in the first step of hybrid CAA, by a random distribution of Kirchhoff's spinning vortices, located in the region between the upper incisors and the lower lip. In this way, one only needs to solve a linear wave equation to generate a sibilant, and therefore avoids the costly large‐scale computations. We show that our proposal can recover the outcomes of hybrid CAA simulations in average, and that it can be applied to generate sibilants /s/ and /z/. Modeling and implementation details of the Kirchhoff vortex distribution in a stabilized finite element code are discussed in the paper, as well as the outcomes of the simulations.

Numerical investigation of effects of incisor angle on production of sibilant /s/

“…To determine the relationship between the positions of the velocity fluctuations, i.e., the assumed aeroacoustic sound sources, and the far-field SPL spectra, instead of the base simulation with constant velocity inlet from the throat, the acoustic simulations with acoustic monopole sources were conducted for the 0° and 30° cases. In the previous acoustic studies, monopole to quadrupole sound sources were used to emulate the sound generated by the turbulent flow 29 , 30 . Therefore, for the simplicity, the monopole sources composed of white noise were applied in the current study at Point 1 (49.1, − 8.4, − 7.7) and Point 2 (58.5, − 7.7, − 4.5), which corresponded to the positions of maximum velocity fluctuations at 10 kHz for both models.…”

Simulation of vowel‐vowel utterances using a 3D biomechanical‐acoustic model

“…For example, to generate a fricative sound, the biomechanical model should be able to form a precise, narrow constriction, which demands a refined tongue mesh with very small elements, and a detailed deformation control. Also, the acoustic model needs to handle turbulent noise 50‐52 …”

“…Also, the acoustic model needs to handle turbulent noise. [50][51][52] Regarding the muscle activation procedure, let us note that the utilized estimation for static vowels based on inversion of stylized articulatory trajectories is not the only option. Alternatives include, for example, the use of articulation data from EMMA or (static and/or real-time) MRI, or acoustic-to-articulatory inversion.…”

Evaluation of Glottal Inverse Filtering Techniques on OPENGLOT Synthetic Male and Female Vowels

“…Voice generation based on articulatory speech synthesis has been significantly improved by considering three-dimensional (3D) source-filter models, surpassing the limitations of their one-dimensional counterparts [1,2]. These advanced models have demonstrated their ability to generate various speech utterances, including vowels [3], diphthongs [4,5], and vowel-consonant-vowel sequences incorporating fricatives [6,7]. Despite these accomplishments, the exploration of expressive voice synthesis using these 3D-based numerical simulations is still in its early stages due to its great complexity.…”