1,833 research outputs found
Waveguide physical modeling of vocal tract acoustics: flexible formant bandwidth control from increased model dimensionality
Digital waveguide physical modeling is often used as an efficient representation of acoustical resonators such as the human vocal tract. Building on the basic one-dimensional (1-D) Kelly-Lochbaum tract model, various speech synthesis techniques demonstrate improvements to the wave scattering mechanisms in order to better approximate wave propagation in the complex vocal system. Some of these techniques are discussed in this paper, with particular reference to an alternative approach in the form of a two-dimensional waveguide mesh model. Emphasis is placed on its ability to produce vowel spectra similar to that which would be present in natural speech, and how it improves upon the 1-D model. Tract area function is accommodated as model width, rather than translated into acoustic impedance, and as such offers extra control as an additional bounding limit to the model. Results show that the two-dimensional (2-D) model introduces approximately linear control over formant bandwidths leading to attainable realistic values across a range of vowels. Similarly, the 2-D model allows for application of theoretical reflection values within the tract, which when applied to the 1-D model result in small formant bandwidths, and, hence, unnatural sounding synthesized vowels
Extreme acoustic anisotropy in crystals visualized by diffraction tensor
Acoustic wave propagation in single crystals, metamaterials and composite
structures is a basic mechanism in acoustic, acousto-electronic and
acousto-optic devices. Acoustic anisotropy of crystals provides a variety of
device performances and application fields, but its role in pre-estimation of
achievable device characteristics and location of crystal orientations with
desired properties is often underestimated. A geometrical image of acoustic
anisotropy can be an important tool in design of devices based on wave
propagation in single crystals or combinations of anisotropic materials. We
propose a fast and robust method for survey and visualization of acoustic
anisotropy based on calculation of the eigenvalues of bulk acoustic wave (BAW)
diffraction tensor (curvature of the slowness surface). The stereographic
projection of these eigenvalues clearly reveals singular directions of BAW
propagation (acoustic axes) in anisotropic media and areas of fast or slow
variation of wave velocities. The method is illustrated by application to three
crystals of different symmetry used in different types of acoustic devices:
paratellurite, lithium niobate, and potassium gadolinium tungstate. The
specific features of acoustic anisotropy are discussed for each crystal in
terms of their potential application in devices. In addition, we demonstrate
that visualization of acoustic anisotropy of lithium niobate helps to find
orientations supporting propagation of high-velocity surface acoustic waves.Comment: 12 pages, preprint submitted to EPJ Plu
Forward sound propagation around seamounts : application of acoustic models to the Kermit-Roosevelt and Elvis seamounts
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2009The Basin Acoustic Seamount Scattering Experiment (BASSEX) of 2004 was conducted
to measure forward-scattering around the Kermit-Roosevelt Seamount Complex in the
Northeast Pacific. The BASSEX experiment was focused on the bathymetric effects on
acoustic propagation, in particular, on direct blockage, horizontal refraction, diffraction,
and scattering by the seamounts. A towed hydrophone array, with 64 sensors cut for
250Hz (3m spacing), was used to measure the signals transmitted from the
aforementioned broadband sources at many locations around the Kermit-Roosevelt and
Elvis seamounts. Utilizing the measured broadband signals from the towed array, the size
of the shadow zone was obtained. The measured data in the BASSEX experiment
strongly support the understanding of the complicated phenomena of sound propagation
around the seamounts. In addition, the experimental data could be used to validate current
2D and 3D theoretical models and develop new models to properly realize the sound
propagation with such complicated phenomena.
In this thesis, the reconciliation between the measured pulse arrivals from the
BASSEX experiment and various two-dimensional (2D) and three-dimensional (3D)
theoretical models is carried out to investigate the physical characteristics of the sound
propagation around seamounts: First, the 2D Parabolic Equation (PE) model and the 2D
ray tracing model are used to reconcile each ray arrival with the BASSEX experiment in
terms of arrival time and grazing angle. We construct a sound speed field database based
on the sound speed profiles from the BASSEX experiment, World Ocean Atlas (WOA)
2005, and CTD casts using the objective analysis.
Second, 3D broadband sound propagation around a conical seamount is
investigated numerically using the 3D spectral coupled-mode model (W. Luo, PhD Thesis,
MIT, 2007). Since the calculation of 3D broadband pulses with the spectral coupledmode
model requires extensive computation time, a parallel program is developed with a
clustered computing system to obtain results in reasonable time. The validation of the 3D
spectral coupled-mode model is performed by a series of comparisons between the
various 2D and 3D models for a shallow-water waveguide. The Kermit-Roosevelt
seamount is modeled by a simple conical seamount for the 3D model. The computed 3D
broadband pulses for the modeled conical seamount are compared with those from the
BASSEX experiment and the 2D PE simulation.
Through this analysis, we examine the limit of the application of the sound
propagation models and improve the efficiency of the 3D sound propagation model using
parallel computing to obtain a broadband pulse in a reasonable amount of time
Acoustic modeling using the digital waveguide mesh
The digital waveguide mesh has been an active area of music acoustics research for over ten years. Although founded in 1-D digital waveguide modeling, the principles on which it is based are not new to researchers grounded in numerical simulation, FDTD methods, electromagnetic simulation, etc. This article has attempted to provide a considerable review of how the DWM has been applied to acoustic modeling and sound synthesis problems, including new 2-D object synthesis and an overview of recent research activities in articulatory vocal tract modeling, RIR synthesis, and reverberation simulation. The extensive, although not by any means exhaustive, list of references indicates that though the DWM may have parallels in other disciplines, it still offers something new in the field of acoustic simulation and sound synth
Fast Numerical Methods for Non-local Operators
[no abstract available
Calculating conical diffraction coefficients
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
- …