[chillingeffect]

It's a combination of several oscillators and complex resonator model.

The oscillator includes the vocal chords as well as a model of the lips for fricatives, plosives, etc.

The resonator includes several major tunable cavities, from the longs to the trachea to the sinuses, nasal cavities and mouth. These resonators form filters called formants which have default configurations for every vowel sound, however they are highly customized for every singer and express a terrific degree of nuance. Synthesis requires a multi-dimensional score somewhat like a speech synthesizer. The score can be dimension-reduced, but it will sound like crap. I would expect it to take about as much time to enter the data as it would to learn to perform it.