370 likes | 461 Views
Influence of Acoustic Loading on the Flow-Induced Oscillations of Single Mass Models of the Human Larynx. Matías Zañartu Salas School of Electrical and Computer Engineering Purdue University. Outline. Introduction Objectives Wave Reflection Analog Model for the Acoustics of the Tracts
E N D
Influence of Acoustic Loading on the Flow-Induced Oscillations of Single Mass Models of the Human Larynx Matías Zañartu Salas School of Electrical and Computer Engineering Purdue University
Outline • Introduction • Objectives • Wave Reflection Analog Model for the Acoustics of the Tracts • Effective Single Degree of Freedom Model of the Vocal Folds • Results of the Coupled Models • Conclusions • Suggestions for Future Research
Motivation • Applications of early models of voice production: • speech synthesis, • speech recognition, • speech coding. • Applications of current research on voice production : • Improve upon previous applications, • Early detection and better treatment of voice pathologies, • Development of bioimplants, • Optimization of voice prosthesis, • Voice enhancements for singers, • Better tools for voice simulation and speech perception, • Phonosurgical modeling.
Voice production system Typical phonation cycle
One-mass model Multi-mass model
Introduction • Forces in phase with the velocity of the tissue (mass) are favorable to phonation. • A “mucosal wave” in the cover of the vocal fold • An inertive impedance in the vocal tract • The relative importance is unknown. • The role of other supraglottal loadings and the subglottal tract is not clear. • One-mass models cannot reach SSO without acoustic loading, since no mucosal wave is present.
Objectives • Model for the acoustics of the tracts: • Subglottal and the supraglottal tracts. • Static representation of non-nasal vowels • Produce synthesized speech • Time domain based • Model of the vocal folds vibration: • One-mass model • Able to produce SSO without acoustic loading • Coupling of the two models: • Role of acoustic loadings • Flow-sound interactions vs. flow-structure
Model for the Acoustics of the Tracts • Wave Reflection Analog Model (Kelly & Lochbaum, 1962; Liljencrants, 1985; Rahim, 1994; Story, 1995) • Originally designed for speech synthesis • Time domain based technique • Instantaneous acoustic pressure and volumetric flow rate at any time in any place • Radiation impedance and different types of energy dissipation • Revealed acoustic differences due to detailed geometries. MRI shapes of the tracts
Sound waves: αk supra Termination impedance Connection with the source model Sound waves: αk sub Wave Reflection Analog
Supraglottal Subglottal αk (subglottal) αk (supraglottal)Rahim, 1994 Loss Factor for each Tract
Evaluation of the complete scheme • Effects of boundary conditions • Closed-open • Closed-closed • Open-open • Effects of radiation impedance • Adjusted magnitude of reflected pressures • Added a positive slope • Effects of the global loss factor • Reduced magnitude and bandwidth of formants • More pronounced in narrow-band formants • Acoustic coupling between tracts • Both linear and non-linear showed poles and zeros • Non-linear approach introduced more variations
Evaluation Tests Basic Approach: Matlab animations:
Wave reflection analog Theoretical complex solution Comparison with theoretical complex solution of the planar wave equation Closed-open uniform tube with termination impedance Theoretical complex solution Piston with at x=0, operating at all frequencies. Pressure measured at x=L Wave reflection analog No losses With losses Closed at x=0, impulse injected at x=0 and t=0. Pressure measured at x=L
F1 F2 F3 Proposed Subglottal Tract Design Spectrum of the acoustic pressure at x=0 x=0 Weibel, 1963 Proposed subglottal tract design Typical subglottal resonances (Ishizaka, 1976; Stevens,2000; Harper, 2000)
One-Mass Model of the Vocal Folds • Based on Fulcher’s model (2005). Upgrades: • Fluid-structure interactions • Fluid-sound interactions • Collision effects • Used Bernoulli’s equation and obstruction theory. • A smooth time-varying ODC resembled the effects of the mucosal wave. • The ODC for converging and diverging glottal shapes were taken from experimental data. • Material properties were taken from previous studies.
SDOF Self-Oscillating Model Symmetric vocal folds Shape comparison M5 shape: Scherer, 2001
Equation of motion • Equation of motion of the mass is given by: • Fp is the pressure force acting on the open cycle, including • Fluid-structure interactions • Fluid-sound interactions • FH are the forces acting during collision, including • Hertz impact forces • Increased damping ratio (thus b) • Upstream pressure force on the surface
Simplified Flow Diagram of Source Model Coupled with the WRA Model Notes:
SDOF Self-Oscillating Model Starting the cycle Maximum opening Maximum collision
Results of the source model with no acoustic loading fo=180 Hz
Evaluation of the model: no load case • Effects of orifice discharge coefficient • Continuous vs. discontinuous ODC functions • ODC modified Q: amplitude and skewing • Without time-varying ODC the model did not reach SSO • Effects of collision forces • Increased the fundamental frequency of oscillation • Reduced of the amplitude • Importance: (1º) Change in damping, (2º) upstream pressure, (3º) Hertz force • Effects discontinuity in the glottal entrance • Minor differences compared with a continuous profile
Results for the Coupled Models • What was the relative importance between fluid-structure interactions and fluid-sound interactions? • What was the role of each tract? • Cases: • Only fluid-structure interactions • Only fluid-sound interactions • Both type of interactions together • Notes: • No time varying ODC meant cd(t)=1 • Subglottal tract + two vocal tract loadings: MRI /i/ and /A/
a b c d MRI vowel /i/Acoustic coupling only fo=170 Hz F1=225 Hz F2=2486 Hz
a b c d MRI vowel /A/Acoustic coupling only fo=190 Hz F1=786 Hz F2=1147 Hz
a b c d MRI vowel /i/Acoustic coupling and time varying ODC fo=170 Hz F1=225 Hz F2=2486 Hz
a b c d MRI vowel /A/Acoustic coupling and time varying ODC fo=190 Hz F1=786 Hz F2=1147 Hz
Remarks • Acoustic loading with no time varying ODC • Large coupling: source and supraglottal tract • Subglottal tract: less pronounced effects in the source • Modified source properties (Q): • Ripple or depressions=> more harmonics. • Changes in fo • Acoustic loading with time varying ODC • Similar with the no time varying ODC case • Results comparable with other studies using high order models (Story, 2002) => Effects of fluid-sound interaction were more significant than the fluid-structure interaction
Results for the Coupled Models • What were the effects of different acoustic loadings in SSO? • Cases • No time varying ODC were considered • Phase plot only • Different loading profiles • Infinitely long tubes • Uniform tubes with variable area and length • MRI vowels • Subglottal tract designs • Cases tested: • Supraglottal tract • Subglottal tract • Both tracts simultaneously
Effects of acoustic loading on SSO Supraglottal and subglottal loadings, with no time varying ODC
Remarks • Effect of supraglottal loading in SSO • It meets inertance theory. • It leads to SSO in relatively narrow shapes (≤1cm2). • The area is the most sensible variable. • Effect of subglottal loading in SSO • It does not meet the inertance theory. • It does not reach to SSO, but shows favorable. • Realistic shapes are comparable to an infinitely long tube. • Its design (shape, boundary conditions, losses) could severely affect phonation. • The effects are combined when using both tracts.
Conclusions • Time domain model for the acoustics of the tracts: • New subglottal attenuation factor • New subglottal tract design • Complete set of tests to evaluate the scheme • Flexible and with multiple applications • Design of a source model for the vocal folds: • One-mass model able to reach SSO without acoustic load • Allowed fluid-structure interactions • Allowed fluid-sound interactions • It was able to illustrate effects only seen in high order models. • Collision effects were significant
Conclusions • Results of the coupled models: non-linear voice production • Effects of the acoustic loading also led to SSO • The effects of the fluid-sound interaction were more significant than the fluid structure interaction • Important changes were observed in the source • The supraglottal and subglottal tracts played different roles • The inertance theory was met only in the vocal tract • The vocal tract was more dominant than the subglottal tract • The subglottal tract reduced the effects introduced by the vocal tract in Q
Suggestions for Future Research • Improvements in the wave reflection analog: • Frequency dependent losses • Tube branching • Other sources of radiation =>Coupling with piriform sinus, nasal tract. =>Better subglottal tract design. • Improvements in the source model: • Pressure distribution codebook • Use interactive high order model (finite element model) • Include perturbation analysis (jitter, shimmer, SHR, etc)
Suggestions for Future Research • Theoretical perspective: • Develop a complete impedance analysis • Interactive state model for the improved source • Experimental perspective: • Use synthetic models of the vocal folds. Measure Q, pup, pdn as function of the acoustic loadings • DIC is suggested, but the procedure should be adapted
Influence of Acoustic Loading on the Flow-Induced Oscillations of Single Mass Models of the Human Larynx Matías Zañartu Salas School of Electrical and Computer Engineering Purdue University