Creaky voice
Creaky voice (also called laryngealisation or, in singing, vocal fry or glottal fry), is a special kind of phonation in which the arytenoid cartilages in the larynx are drawn together; as a result, the vocal folds are compressed rather tightly, becoming relatively slack and compact, and forming a large, irregularly vibrating mass. The frequency of the vibration is very low (20–50 pulses per second, about two octaves below normal voice) and the airflow through the glottis is very slow. A slight degree of laryngealisation, occurring e.g. in some Korean consonants is called "stiff voice".
There is some argument among music instructors as to whether or not this is an actual register as it can be used to add a raspy sound to other registers. By putting less amount of air on the cords than is needed for a clear tone of the pitch you are going for, the tone breaks up and becomes a rasp. Many Nu Metal singers use this technique to create a screaming sound. One example is Chester Bennington of Linkin Park.
The Danish prosodic feature stød is an example of a form of laryngealisation that has a phonemic function.
Creaky voice manifests itself in the idiolects of some American English speakers, particularly at the beginnings of sentences that the speaker wishes to "soft-pedal". This phenomenon is more prominent among female American English speakers than among male speakers.
This vocal style has been used by singers in Africa and Asia in order to produce multiple notes simultaneously with their voice.[1]
It can also occur accidentally when the speaker's throat is tired.