1. An apparatus for natural inter-viseme animation of a 3D model driven by speech recognition, comprising: a speech recognition engine that identifies phonemes in a sequence of speech; and a processor programmed to associate phonemes with corresponding visemes which represent facial expressions in said 3D model; said processor programmed to determine and apply limitations to any of velocity and acceleration of a normalized parameter vector; said processor programmed to map each element of said parameter vector to animation node outputs of said 3D model.