| 1. |
- Arnela, Marc, et al.
(författare)
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A semi-polar grid strategy for the three-dimensional finite element simulation of vowel-vowel sequences
- 2017
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Ingår i: Proceedings of the Annual Conference of the International Speech Communication Association, INTERSPEECH 2017. - : The International Speech Communication Association (ISCA). ; , s. 3477-3481
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Konferensbidrag (refereegranskat)abstract
- Three-dimensional computational acoustic models need very detailed 3D vocal tract geometries to generate high quality sounds. Static geometries can be obtained from Magnetic Resonance Imaging (MRI), but it is not currently possible to capture dynamic MRI-based geometries with sufficient spatial and time resolution. One possible solution consists in interpolating between static geometries, but this is a complex task. We instead propose herein to use a semi-polar grid to extract 2D cross-sections from the static 3D geometries, and then interpolate them to obtain the vocal tract dynamics. Other approaches such as the adaptive grid have also been explored. In this method, cross-sections are defined perpendicular to the vocal tract midline, as typically done in 1D to obtain the vocal tract area functions. However, intersections between adjacent cross-sections may occur during the interpolation process, especially when the vocal tract midline quickly changes its orientation. In contrast, the semi-polar grid prevents these intersections because the plane orientations are fixed over time. Finite element simulations of static vowels are first conducted, showing that 3D acoustic wave propagation is not significantly altered when the semi-polar grid is used instead of the adaptive grid. The vowel-vowel sequence [ɑi] is finally simulated to demonstrate the method.
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| 2. |
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| 3. |
- Arnela, Marc, et al.
(författare)
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Finite element generation of vowel sounds using dynamic complex three-dimensional vocal tracts
- 2016
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Ingår i: Proceedings of the 23rd international congress on sound and vibration. - : INT INST ACOUSTICS & VIBRATION. - 9789609922623
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Konferensbidrag (refereegranskat)abstract
- Three-dimensional (3D) numerical simulations of the vocal tract acoustics require very detailed vocal tract geometries in order to generate good quality vowel sounds. These geometries are typically obtained from Magnetic Resonance Imaging (MRI), from which a volumetric representation of the complex vocal tract shape is obtained. Static vowel sounds can then be generated using a finite element code, which simulates the propagation of acoustic waves through the vocal tract when a given train of glottal pulses is introduced at the glottal cross-section. A more challenging problem to solve is that of generating dynamic vowel sounds. On the one hand, the acoustic wave equation has to be solved in a computational domain with moving boundaries, which entails some numerical difficulties. On the other hand, the finite element meshes where acoustic wave propagation is computed have to move according to the dynamics of these very complex vocal tract shapes. In this work this problem is addressed. First, the acoustic wave equation in mixed form is expressed in an Arbitrary Lagrangian-Eulerian (ALE) framework to account for the vocal tract wall motion. This equation is numerically solved using a stabilized finite element approach. Second, the dynamic 3D vocal tract geometry is approximated by a finite set of cross-sections with complex shape. The time-evolution of these cross-sections is used to move the boundary nodes of the finite element meshes, while inner nodes are computed through diffusion. Some dynamic vowel sounds are presented as numerical examples.
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| 4. |
- Arnela, Marc, et al.
(författare)
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Influence of lips on the production of vowels based on finite element simulations and experiments
- 2016
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 139:5, s. 2852-2859
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Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional (3-D) numerical approaches for voice production are currently being investigated and developed. Radiation losses produced when sound waves emanate from the mouth aperture are one of the key aspects to be modeled. When doing so, the lips are usually removed from the vocal tract geometry in order to impose a radiation impedance on a closed cross-section, which speeds up the numerical simulations compared to free-field radiation solutions. However, lips may play a significant role. In this work, the lips' effects on vowel sounds are investigated by using 3-D vocal tract geometries generated from magnetic resonance imaging. To this aim, two configurations for the vocal tract exit are considered: with lips and without lips. The acoustic behavior of each is analyzed and compared by means of time-domain finite element simulations that allow free-field wave propagation and experiments performed using 3-D-printed mechanical replicas. The results show that the lips should be included in order to correctly model vocal tract acoustics not only at high frequencies, as commonly accepted, but also in the low frequency range below 4 kHz, where plane wave propagation occurs.
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| 5. |
- Arnela, Marc, et al.
(författare)
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Influence of vocal tract geometry simplifications on the numerical simulation of vowel sounds
- 2016
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Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 140:3, s. 1707-1718
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Tidskriftsartikel (refereegranskat)abstract
- For many years, the vocal tract shape has been approximated by one-dimensional (1D) area functions to study the production of voice. More recently, 3D approaches allow one to deal with the complex 3D vocal tract, although area-based 3D geometries of circular cross-section are still in use. However, little is known about the influence of performing such a simplification, and some alternatives may exist between these two extreme options. To this aim, several vocal tract geometry simplifications for vowels [ɑ], [i], and [u] are investigated in this work. Six cases are considered, consisting of realistic, elliptical, and circular cross-sections interpolated through a bent or straight midline. For frequencies below 4–5 kHz, the influence of bending and cross-sectional shape has been found weak, while above these values simplified bent vocal tracts with realistic cross-sections are necessary to correctly emulate higher-order mode propagation. To perform this study, the finite element method (FEM) has been used. FEM results have also been compared to a 3D multimodal method and to a classical 1D frequency domain model.
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| 6. |
- Arnela, Marc, et al.
(författare)
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MRI-based vocal tract representations for the three-dimensional finite element synthesis of diphthongs
- 2019
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Ingår i: IEEE Transactions on Audio, Speech, and Language Processing. - : IEEE Press. - 1558-7916 .- 1558-7924. ; 27:12, s. 2173-2182
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of diphthongs in three-dimensions (3D) involves the simulation of acoustic waves propagating through a complex 3D vocal tract geometry that deforms over time. Accurate 3D vocal tract geometries can be extracted from Magnetic Resonance Imaging (MRI), but due to long acquisition times, only static sounds can be currently studied with an adequate spatial resolution. In this work, 3D dynamic vocal tract representations are built to generate diphthongs, based on a set of cross-sections extracted from MRI-based vocal tract geometries of static vowel sounds. A diphthong can then be easily generated by interpolating the location, orientation and shape of these cross-sections, thus avoiding the interpolation of full 3D geometries. Two options are explored to extract the cross-sections. The first one is based on an adaptive grid (AG), which extracts the cross-sections perpendicular to the vocal tract midline, whereas the second one resorts to a semi-polar grid (SPG) strategy, which fixes the cross-section orientations. The finite element method (FEM) has been used to solve the mixed wave equation and synthesize diphthongs [${\alpha i}$] and [${\alpha u}$] in the dynamic 3D vocal tracts. The outputs from a 1D acoustic model based on the Transfer Matrix Method have also been included for comparison. The results show that the SPG and AG provide very close solutions in 3D, whereas significant differences are observed when using them in 1D. The SPG dynamic vocal tract representation is recommended for 3D simulations because it helps to prevent the collision of adjacent cross-sections.
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| 7. |
- Dabbaghchian, Saeed, et al.
(författare)
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Reconstruction of vocal tract geometries from biomechanical simulations
- 2018
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - : John Wiley & Sons. - 2040-7939 .- 2040-7947.
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Tidskriftsartikel (refereegranskat)abstract
- Medical imaging techniques are usually utilized to acquire the vocal tract geometry in 3D, which may then be used, eg, for acoustic/fluid simulation. As an alternative, such a geometry may also be acquired from a biomechanical simulation, which allows to alter the anatomy and/or articulation to study a variety of configurations. In a biomechanical model, each physical structure is described by its geometry and its properties (such as mass, stiffness, and muscles). In such a model, the vocal tract itself does not have an explicit representation, since it is a cavity rather than a physical structure. Instead, its geometry is defined implicitly by all the structures surrounding the cavity, and such an implicit representation may not be suitable for visualization or for acoustic/fluid simulation. In this work, we propose a method to reconstruct the vocal tract geometry at each time step during the biomechanical simulation. Complexity of the problem, which arises from model alignment artifacts, is addressed by the proposed method. In addition to the main cavity, other small cavities, including the piriform fossa, the sublingual cavity, and the interdental space, can be reconstructed. These cavities may appear or disappear by the position of the larynx, the mandible, and the tongue. To illustrate our method, various static and temporal geometries of the vocal tract are reconstructed and visualized. As a proof of concept, the reconstructed geometries of three cardinal vowels are further used in an acoustic simulation, and the corresponding transfer functions are derived.
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| 8. |
- Dabbaghchian, Saeed, et al.
(författare)
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SIMPLIFICATION OF VOCAL TRACT SHAPES WITH DIFFERENT LEVELS OF DETAIL
- 2015
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Ingår i: Proceedings of the 18th International Congress of Phonetic Sciences. Glasgow, UK. - : University of Glasgow. - 9780852619414 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- We propose a semi-automatic method to regenerate simplified vocal tract geometries from very detailed input (e.g. MRI-based geometry) with the possibility to control the level of detail, while maintaining the overall properties. The simplification procedure controls the number and organization of the vertices in the vocal tract surface mesh and can be assigned to replace complex cross-sections with regular shapes. Six different geometry regenerations are suggested: bent or straight vocal tract centreline, combined with three different types of cross-sections; namely realistic, elliptical or circular. The key feature in the simplification is that the cross-sectional areas and the length of the vocal tract are maintained. This method may, for example, be used to facilitate 3D finite element method simulations of vowels and diphthongs and to examine the basic acoustic characteristics of vocal tract in printed physical replicas. Furthermore, it allows for multimodal solutions of the wave equation.
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| 9. |
- Dabbaghchian, Saeed, et al.
(författare)
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Simulation of vowel-vowel utterances using a 3D biomechanical-acoustic model
- 2021
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Ingår i: International Journal for Numerical Methods in Biomedical Engineering. - Wiley : Wiley-Blackwell. - 2040-7939 .- 2040-7947. ; 37:1
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Tidskriftsartikel (refereegranskat)abstract
- A link is established between biomechanical and acoustic 3D models for the numerical simulation of vowel-vowel utterances. The former rely on the activation and contraction of relevant muscles for voice production, which displace and distort speech organs. However, biomechanical models do not provide a closed computational domain of the 3D vocal tract airway where to simulate sound wave propagation. An algorithm is thus proposed to extract the vocal tract boundary from the surrounding anatomical structures at each time step of the transition between vowels. The resulting 3D geometries are fed into a 3D finite element acoustic model that solves the mixed wave equation for the acoustic pressure and particle velocity. An arbitrary Lagrangian-Eulerian framework is considered to account for the evolving vocal tract. Examples include six static vowels and three dynamic vowel-vowel utterances. Plausible muscle activation patterns are first determined for the static vowel sounds following an inverse method. Dynamic utterances are then generated by linearly interpolating the muscle activation of the static vowels. Results exhibit nonlinear trajectory of the vocal tract geometry, similar to that observed in electromagnetic midsagittal articulography. Clear differences are appreciated when comparing the generated sound with that obtained from direct linear interpolation of the vocal tract geometry. That is, interpolation between the starting and ending vocal tract geometries of an utterance, without resorting to any biomechanical model.
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| 10. |
- Dabbaghchian, Saeed, et al.
(författare)
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Synthesis of vowels and vowel-vowel utterancesusing a 3D biomechanical-acoustic model
- 2018
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Ingår i: IEEE/ACM Transactions on Audio, Speech, and Language Processing. - 2329-9290.
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Tidskriftsartikel (refereegranskat)abstract
- A link is established between a 3D biomechanicaland acoustic model allowing for the umerical synthesis of vowelsounds by contraction of the relevant muscles. That is, thecontraction of muscles in the biomechanical model displacesand deforms the articulators, which in turn deform the vocaltract shape. The mixed wave equation for the acoustic pressureand particle velocity is formulated in an arbitrary Lagrangian-Eulerian framework to account for moving boundaries. Theequations are solved numerically using the finite element method.Since the activation of muscles are not fully known for a givenvowel sound, an inverse method is employed to calculate aplausible activation pattern. For vowel-vowel utterances, two different approaches are utilized: linear interpolation in eithermuscle activation or geometrical space. Although the former isthe natural choice for biomechanical modeling, the latter is usedto investigate the contribution of biomechanical modeling onspeech acoustics. Six vowels [ɑ, ə, ɛ, e, i, ɯ] and three vowel-vowelutterances [ɑi, ɑɯ, ɯi] are synthesized using the 3D model. Results,including articulation, formants, and spectrogram of vowelvowelsounds, are in agreement with previous studies.Comparingthe spectrogram of interpolation in muscle and geometrical spacereveals differences in all frequencies, with the most extendeddifference in the second formant transition.
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