Modulation of the glottal airspace is accomplished with a kinematic representation of the vibrating portion of the vocal fold medial surfaces, in which time-varying surface displacements are superimposed onto a postural configuration. The prephonatory posture is defined by superior and inferior values of separation at the vocal processes and by a bulging parameter that provides curvature to the medial surface. The vocal fold length (antero-posterior dimension of the surface along midline) and thickness (inferior-superior extent of the surface) can be specified to be characteristic of a particular talker. The time-varying vibratory displacement is based on a summation of translational and rotational modes in the vertical dimension and a ribbon mode in the antero-posterior dimension. The amplitude of vibration and mucosal wave velocity are governed by rules as described in Titze (2006).