A nonlinear digital feedback oscillator based vibrato control model for singing synthesis

By investigating the production mechanism of vocal vibrato, a nonlinear digital feedback oscillator based vibrato control model was proposed. The feedback oscillation behaviour of laryngeal agonist-antagonist muscles is modeled by a self-oscillated feedback oscillator, in which a nonlinear limiter is introduced to describe the physical limitation of muscle activity. The proposed model could provide a flexible control over the following dynamic characteristics of vocal vibrato: (1) the attack and release; (2) irregularities of the vibrato rate and extent; (3) the increasing vibrato rate at the end of a note. Psychoacoustic experiments were conducted to evaluate the model and to demonstrate how these characteristics influence singing perception. Experimental results show that the dynamic characteristics affect the quality of vocal vibrato. Moreover, introducing attack and release could significantly improve the naturalness of synthetic singing voice.