Yes and no. Perceptually, you don't really need to model everything to get convincing speech sounds. Most of the realism actually comes from performance, and no

Yes and no. Perceptually, you don't really need to model everything to get convincing speech sounds. Most of the realism actually comes from performance, and not the mathematical model. In a way, lips and mouth are accounted for here, but in a more abstract away. The KL model approximates the vocal tract as a series of cylindrical tubes with varying diameters. Segments of the tubes actually correspond to things like the tongue and mouth somewhat. In this model there is a really neat tongue control that manipulates these segments. It's quite expressive! This model is a 1d waveguide, so it doesn't account for things like the curvature of the tract. More modern vocal modelling techniques include implementing a 2-dimensional waveguide, which does allow for this control.