How does it all work together to make a voice?
The physiology (functioning) of voice production is exceedingly complex. Production of voice begins in the cerebral cortex of the brain. Many other brain centers are involved in sending appropriate impulses to the nerves and muscles required for phonation. The brain also receives tactile (feeling) and auditory (hearing) feedback information and makes adjustments in order to control the voice sounds produced.
Phonation (using the vocal folds to make sound) requires interaction among the power source, oscillator and resonator. The voice may be likened to a brass instrument such as a trumpet. Power is generated by the chest, abdomen and back musculature producing a high pressure air stream. The trumpeter's lips open and close against the mouth piece producing a buzz similar to the sound produced by the vocal folds. This sound then passes through the trumpet which has resonance characteristics that shape the sound we associate with trumpet music. The non-mouthpiece portion of a brass instrument is analogous to the supraglottic vocal tract.
During phonation, rapid, complex adjustments of the infraglottic system are necessary because the resistance changes almost continuously as the glottis closes, opens and changes shape. At the beginning of each phonatory cycle, the vocal folds are together. As air pressure builds up against them, they are pushed apart and snap back together. Sound is actually produced by the closing of the vocal folds, in a manner similar to the sound generated by hand clapping. Contrary to popular opinion, the vocal folds are not chords that vibrate like piano or guitar strings. Also like hand clapping, the more forcefully the vocal folds snap together, the louder the sound; and the more frequently they open and close, the higher the pitch.
The sound produced by the vocal folds is a complex tone. As it passes through the supraglottic vocal tract, the pharynx, oral cavity and nasal cavity act as a series of interconnected resonators, more complex than a trumpet because the walls and shape are flexible. The ultimate voice quality is determined as the sound produced by the vocal folds passes through the resonator.