The process of producing a voice is called “phonation.” To begin phonating, speakers must first approximate the vocal folds so that they are close together and block the airway. Air pressure from the lungs next blows them apart (so that a puff of air travels through the glottis), and then ongoing rush of air creates a negative pressure between the folds that sucks them back together. These opening-and-closing movements interrupt airflow from the lungs, producing the changes in the air pressure that we hear as sound.