Phonation is the production of sound by structures in the upper respiratory tract.
During exhalation, air passes from the lungs through the larynx. Muscles in the larynx can act to move the arytenoid cartilages that then move the cords. The cords are pushed together and air passes between them in such a way as to make them vibrate, creating sound. Greater tension in the vocal folds creates more rapid vibrations and higher pitched sounds. Lower tension causes slower vibration and a lower pitch. Sounds can also be altered by other factors: high pressure creates louder sound, longer folds produce lower pitch sounds, and shorter folds produce higher pitch. Structures in the oral and nasal cavities can also modify the sounds produced by the vocal folds.