While sample-playback synthesis is especially effective for percussion instruments that are supposed to play ``in the background,'' some form of parametrization is needed for more expressive performances, or for highly variable percussion instruments such as the Indian tabla. Highly efficient computational models of 2D membranes and 3D volumes may be built using the digital waveguide mesh [147,524,522,525]. More recently, Lauri and Välimäki have developed a frequency-warping approach to compensating for dispersive wave propagation in a variety of mesh types [401,402,404]. The 2001 thesis of Bilbao  provides a unified view of the digital waveguide mesh and wave digital filters  as particular classes of energy invariant finite difference schemes . The problem of modeling diffusion at a mesh boundary was addressed by .