Digital Waveguide Method And Its Application In Vocal Tract Modeling

The digital waveguide method is a theory that describes the process of wavepropagation in space. It uses mathematical algorithm to describe how sound isproduced and propagate in real-world sound. The1D digital waveguide model can besimply shown as a series of cylindrical tubes along a straight axis, which have differentradius. When the wave propagation in width direction of the tract is taken intoconsideration, this1D digital waveguide model can be extended to a2D digitalwaveguide mesh (DWM), which can be applied to a3D model.The main work contained in this thesis is to obtain2D DWM from the original1Dmodel. A2D DWM is configured as a model of human vocal tract, such that all theshape characteristics contained are set within the width of the mesh. Wave propagationand reflection is simulated in two directions, one is along the tract from the glottis tothe lips, the other is across the tract between the two inner walls. In this way, the2Dmodel can remove plane-wave limitations inherent in the1D model. To achieve thesegoals, this thesis has finished the following tasks:First, the thesis gives a detailed introduction to the theory of wave propagation inspace and obtains numerical simulation of1D wave equation. Then1D case can beextended to a more general2D model by using wave scattering method and FiniteDifference Time-Domain (FDTD) approximation, so that the numerical simulation of2D wave equation can be obtained.Second, the vocal tract model can be simulated by using1D digital waveguidemethod. Combined with wave propagation in space, the detailed process of wavepropagation in vocal tract can then be achieved. The1D model can be extended to2Dmodel by considering the effects of vocal walls to wave propagation.Third, the1D and2D digital waveguide model can be used in speech synthesis application. By introducing the LF glottal wave as excitation, some simple vowels canbe synthesized, which proves the effectiveness of digital waveguide methods.