The term phonation has slightly different meanings depending on the subfield of phonetics. Among some phoneticians, phonation is the process by which the vocal folds produce certain sounds through quasi-periodic vibration. This is the definition used among those who study laryngeal anatomy and physiology and speech production in general. Other phoneticians, though, call this process voicing, and they use the term phonation to refer to any oscillatory state of any part of the larynx that modifies the airstream, of which voicing is just one example. As such, voiceless and supra-glottal phonation are included under this definition, which is common in the field of linguistic phonetics.