AskDefine | Define phonation

Dictionary Definition

phonation n : the sound made by the vibration of vocal folds modified by the resonance of the vocal tract; "a singer takes good care of his voice"; "the giraffe cannot make any vocalizations" [syn: voice, vocalization, vocalisation, vox]

User Contributed Dictionary

English

Noun

  1. The process of producing vocal sound by the vibration of the vocal folds that is in turn modified by the resonance of the vocal tract.

Synonyms

Extensive Definition

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.
To others, though, this process is called voicing. Phonation refers instead to any oscillatory state of any part of the larynx that modifies the airstream, of which voicing is just one. As such, voiceless and supra-glottal phonation are included under this definition but are not considered types of phonation under the former definition. This definition is common in the field of linguistic phonetics.

The phonatory process

The phonatory process, or voicing, occurs when air is expelled from the lungs through the glottis, creating a pressure drop across the larynx. When this drop becomes sufficiently large, the vocal folds start to oscillate. The minimum pressure drop required to achieve phonation is called the phonation threshold pressure, and for humans with normal vocal folds, it is approximately 2-3 cm H2O. The motion of the vocal folds during oscillation is mostly in the lateral direction, though there is also some superior component as well. However, there is almost no motion along the length of the vocal folds. The oscillation of the vocal folds serves to modulate the pressure and flow of the air through the larynx, and this modulated airflow is the main component of the sound of most voiced phones.
The sound that the larynx produces is a harmonic series. In other words, it consists of a fundamental tone (called the fundamental frequency, the main acoustic cue for the percept pitch) accompanied by harmonic overtones which are multiples of the fundamental frequency . According to the Source-Filter Theory, the resulting sound excites the resonance chamber that is the vocal tract to produce the individual speech sounds.
The vocal folds will not oscillate if they are not sufficiently close to one another, are not under sufficient tension or under too much tension, or if the pressure drop across the larynx is not sufficiently large. In linguistics, a phone is called voiceless if there is no phonation during its occurrence..
Fundamental frequency, the main acoustic cue for the percept pitch, can be varied through a variety of means. Large scale changes are accomplished by increasing the tension in the vocal folds through contraction of the cricothyroid muscle. Smaller changes in tension can be effected by contraction of the thyroarytenoid muscle or changes in the relative position of the thyroid and cricoid cartilages, as may occur when the larynx is lowered or raised, either volitionally or through movement of the tongue to which the larynx is attached via the hyoid bone. These two theories are not in contention with one another and it is quite possible that both theories are true and operating simultaneously to initiate and maintain vibration. A third theory, the neurochronaxic theory, was in considerable vogue in the 1950s, but has since been largely discredited.

The myoelastic theory

This theory states that when the vocal cords are closed and breath pressure is applied to them, the cords remain closed until the pressure beneath them--the subglottic pressure--is sufficient to push them apart, allowing air to escape and reducing the pressure enough for the muscle tension to pull the folds back together again. Pressure builds up once again until the cords are pushed apart, and the whole cycle keeps repeating itself. The rate at which the cords open and close--the number of cycles per second--determines the pitch of the phonation. is essentially a combination of the two described above and is currently the most accepted theory of phonation by voice and speech scientists and vocologists.

Phonation as the state of the glottis

In linguistic phonetic treatments of phonation, such as those of Peter Ladefoged, phonation was considered to be a matter of points on a continuum of tension and closure of the vocal cords. More intricate mechanisms were occasionally described, but they were difficult to investigate, and until recently the state of the glottis and phonation were considered to be nearly synonymous.
If the vocal cords are completely relaxed, with the arytenoid cartilages apart for maximum airflow, the cords do not vibrate. This is voiceless phonation, and is extremely common with obstruents. If the arytenoids are pressed together for glottal closure, the vocal cords block the airstream, producing stop sounds such as the glottal stop. In between there is a sweet spot of maximum vibration. This is modal voice, and is the normal state for vowels and sonorants in all the world's languages. However, the aperture of the arytenoid cartilages, and therefore the tension in the vocal cords, is one of degree between the end points of open and closed, and there are several intermediate situations utilized by various languages to make contrasting sounds.
  1. glottal (the vocal cords), producing the distinctions described above
  2. ventricular (the 'false vocal cords', partially covering and damping the glottis)
  3. arytenoid (sphincteric compression forwards and upwards)
  4. epiglotto-pharyngeal (retraction of the tongue and epiglottis, potentially closing onto the pharyngeal wall)
  5. raising or lowering of the entire larynx
  6. narrowing of the pharynx
Until the development of fiber-optic laryngoscopy, the full involvement of the larynx during speech production was not observable, and the interactions among the six laryngeal articulators is still poorly understood. However, at least two supra-glottal phonations appear to be widespread in the world's languages. These are harsh voice ('ventricular' or 'pressed' voice), which involves overall constriction of the larynx, and faucalized voice ('hollow' or 'yawny' voice), which involves overall expansion of the larynx. The term "register" may be used for several distinct aspects of the human voice::
Four combinations of these elements are identified in speech pathology: the vocal fry register, the modal register, the falsetto register, and the whistle register.

References

phonation in Breton: Doare fonadur
phonation in Czech: Znělost
phonation in German: Artikulation (Linguistik)
phonation in Spanish: Fonación
phonation in French: Phonation
phonation in Indonesian: Artikulasi
phonation in Hebrew: קוליות העיצורים
phonation in Hungarian: Artikuláció
phonation in Dutch: Articulatie
phonation in Japanese: 発声
phonation in Norwegian Nynorsk: Artikulasjon
phonation in Polish: Artykulacja (fonetyka)
phonation in Portuguese: Fonação
phonation in Romanian: Fonaţie
phonation in Russian: Фонация
phonation in Serbian: Артикулација
phonation in Swedish: Fonation
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