Digital Waveguide Modeling of the Vocal Tract

In his thesis [Cook 1990], Perry Cook describes a method of vocal tract modeling superior to the previously described formant-filter based approach. The method involves approximating the vocal tract by a series of acoustic tube sections, each with a radius that varies from one vowel sound to the next. As shown in [Cook 1990], the radii of adjacent tube sections govern the transmission and reflection of acoustic energy at the junction between such sections. For each tube section, discrete-time delay elements are used to model the forward- and reverse-traveling wave components of the digital waveguide simulation⁴. Between the delay elements, a scattering junction is used to handle the change in radius from one tube section to the next. A block diagram is shown in Figure 3.

Figure 3: Digital waveguide model of the human vocal tract, with scattering junctions between adjacent tube sections to account for changing radii (adapted from [Cook 1990]).