Articulatory speech synthesis based on fractional delay waveguide filters

An extension to the traditional Kelly-Lochbaum vocal tract model is introduced. In the new model not only the diameter but also the length of each tube section can be continuously adjusted. This is achieved by using fractional delay filter techniques such as interpolation and deinterpolation. The filter structure consisting of bidirectional delay lines (digital waveguides) and interpolated ports that connect two or more waveguide sections together is called a fractional delay waveguide filter (FDWF). The interpolated version of the two-port scattering junction is presented and a technique for analyzing the degradation due to approximation errors in interpolation and deinterpolation is described. It is shown that when an FDWF structure with Lagrange interpolation is used a vocal tract model needs to be implemented using oversampling. For example, a sampling rate of 22 kHz is adequate for producing high-quality synthetic sounds at a 5 kHz bandwidth.