FIG. 22.  A simplified low-dimensionality model of the vocal tract (Coker, 1976) permits the lips to open (W) or protrude (L); the tongue body to be raised (Y) or be backed (X) or be bunched for a velar closure (K); the tongue tip to be raised with respect to the body (B) or moved forward (R); the jaw to be raised, and the velum to open a path to the nose (N). The sound generating properties of the larynx are controlled by subglottal pressure (P), static glottal opening (G), and vocal cord stiffness (Q).