Phonation

Wikipedia, the free encyclopedia - Cite This Source

Phonation (also voice quality) is 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. It takes place in the larynx when the vocal folds are brought together and breath pressure is applied to them in such a way that vibration ensues causing an audible source of acoustic energy, i.e., sound, which can then be modified by the articulatory actions of the rest of the vocal apparatus. The vocal folds are brought together primarily by the action of the interarytenoid muscles, which pull the arytenoid cartilages together.

Phonation has traditionally been seen as one dimension of phonetic voicing, the degree of glottal tension. (A second dimension of voicing is timing, called voice onset time, or "VOT".)

However, with recent advances in imaging technology, it has become apparent that in many languages phonation involves more than just the glottis.

The phonatory process

A voiced sound is produced when air expelled from the lungs causes the vocal folds to vibrate. This produces a fundamental tone accompanied by several non-harmonic overtones. The resulting sound is modified by movements in the vocal tract, by the volume of the airflow and by the degree of constriction of the vocal cords. (During speech the flow of air is relatively small because of constrictions of the vocal cords.) Vowels are usually voiced, as are many consonants.

If the vocal folds are lax and not sufficiently close to vibrate, then the sound (usually a consonant) is voiceless.

The vocal vibration is varied to produce intonation and tone. This is accomplished by varying the pressure of the air column under the glottis as well as the tension in the vocal folds themselves. These actions produce changes in the frequency of vocal-cord vibration, which generates the fundamental pitch of the voice. Tone and intonation are not conveyed well by voiceless sounds, with their lax vocal folds, but the changes in airflow are still audible.

There are currently two main theories as to how vibration of the vocal folds is initiated: the myoelastic theory and the aerodynamic theory. 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.

The aerodynamic theory

This theory is based on the Bernoulli effect. The theory states that breath is flowing through the glottis while the arytenoid cartilages are being pulled together by the action of the interarytenoid muscles. Due to the Bernouilli Effect, the breath flowing past the vocal folds causes them to be sucked into vibration before the arytenoids are fully together. When the arytenoids have been pulled together, this same air flow sucks the glottis closed, thus cutting off the air flow until breath pressure pushes the folds apart and the flow starts up again, causing the cycles to repeat.

The neurochronaxic theory

This theory states that the frequency of the vocal fold vibration is determined by the chronaxy of the recurrent nerve, and not by breath pressure or muscular tension. Advocates of this theory thought that every single vibration of the vocal folds was due to an impulse from the recurrent laryngeal nerves and that the acoustic center in the brain regulated the speed of vocal fold vibration.

Phonation as the state of the glottis

In classic 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.

For example, Gujarati has vowels with a partially lax phonation called breathy voice or murmured, while Burmese has vowels with a partially tense phonation called creaky voice or laryngealized. Both of these phonations have dedicated IPA diacritics, an under-umlaut and under-tilde. The Jalapa dialect of Mazatec is unusual in contrasting both with modal voice in a three-way distinction. (Note that Mazatec is a tonal language, so the glottis is making several tonal distinctions simultaneously with the phonation distinctions.)

	Mazatec
breathy voice	[ja̤]	he wears
modal voice	[já]	tree
creaky voice	[ja̰]	he carries

Note: There was an editing error in the source of this information. The latter two translations may have been mixed up.

Javanese does not have modal voice in its plosives, but contrasts two other points along the phonation scale, with more moderate departures from modal voice, called slack voice and stiff voice. The "muddy" consonants in Shanghainese are slack voice; they contrast with tenuis and aspirated consonants.

Although each language may be somewhat different, it is convenient to classify these degrees of phonation into discrete categories. A series of seven alveolar plosives, with phonations ranging from an open/lax to a closed/tense glottis, are:

Open glottis	[t]	voiceless (full airstream)
	[d̤]	breathy voice
	[d̥]	slack voice
Sweet spot	[d]	modal voice (maximum vibration)
	[d̬]	stiff voice
	[d̰]	creaky voice
Closed glottis	[ʔ͡t]	glottal closure (blocked airstream)

The IPA diacritics under-ring and subscript wedge, commonly called "voiceless" and "voiced", are sometimes added to the symbol for a voiced sound to indicate more lax/open (slack) and tense/closed (stiff) states of the glottis, respectively. (Ironically, adding the 'voicing' diacritic to the symbol for a voiced consonant indicates less modal voicing, not more, because a modally voiced sound is already fully voiced, at its sweet spot, and any further tension in the vocal cords dampens their vibration.)

Alsatian, like several Germanic languages, has a typologically unusual phonation in its stops. The consonants transcribed (ambiguously called "lenis") are partially voiced: The vocal cords are positioned as for voicing, but do not actually vibrate. That is, they are technically voiceless, but without the open glottis usually associated with voiceless stops. They contrast with both modally voiced /b, d, ɡ/ and modally voiceless /p, t, k/ in French borrowings, as well as aspirated /kʰ/ word initially.

Unaccompanied phonation

It has long been noted that in many languages, both phonologically and historically, the glottal consonants do not behave like other consonants. Phonetically, they have no manner or place of articulation other than the state of the glottis: glottal closure for [ʔ], breathy voice for [ɦ], and open airstream for [h]. Some phoneticians have described these sounds as neither glottal nor consonantal, but instead as instances of pure phonation, at least in many European languages. However, in Semitic languages they do appear to be glottal in place.

Supra-glottal phonation

In the last few decades it has become apparent that phonation may involve the entire larynx, with as many as six valves and muscles working either independently or together. From the glottis upward, these articulations are:

glottal (the vocal cords), producing the distinctions described above
ventricular (the 'false vocal cords', partially covering and damping the glottis)
arytenoid (sphincteric compression forwards and upwards)
epiglotto-pharyngeal (retraction of the tongue and epiglottis, potentially closing onto the pharyngeal wall)
raising or lowering of the entire larynx
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 Bor dialect of Dinka has contrastive modal, breathy, faucalized, and harsh voice in its vowels, as well as three tones. The ad hoc diacritics employed in the literature are a subscript double quotation mark for faucalized voice, [a͈], and underlining for harsh voice, [a]. Examples are,

Voice	modal	breathy	harsh	faucalized
Bor Dinka	ʨìt̪	ʨì̤t̪	ʨìt̪	ʨì͈t̪
	diarrhea	go ahead	scorpions	to swallow

Other languages with these contrasts are Bai (modal, breathy, and harsh voice), Kabiye (faucalized and harsh voice, previously seen as ±ATR), Somali (breathy and harsh voice).

Elements of laryngeal articulation or phonation may occur widely in the world's languages as phonetic detail even when not phonemically contrastive. For example, simultaneous glottal, ventricular, and arytenoid activity (for something other than epiglottal consonants) has been observed in Tibetan, Korean, Nuuchahnulth, Nlaka’pamux, Thai, Sui, Amis, Pame, Arabic, Tigrinya, Cantonese, and Yi.

Phonation in familiar languages

In languages such as French, all obstruents occur in pairs, one modally voiced and one voiceless.

In English, every voiced fricative corresponds to a voiceless one. For the pairs of English plosives, however, the distinction is better specified as voice onset time rather than simply voice: In initial position /b d g/ are only partially voiced (voicing begins during the hold of the consonant), while /p t k/ are aspirated (voicing doesn't begin until well after its release).

Certain English morphemes have voiced and voiceless allomorphs, such as the plural, verbal, and possessive endings spelled -s (voiced in kids /kɪdz/ but voiceless in kits /kɪts/) and the past-tense ending spelled -ed (voiced in buzzed /bʌzd/ but voiceless in fished /fɪʃt/.

A few European languages, such as Finnish, have no phonemically voiced obstruents but pairs of long and short consonants instead. Outside of Europe, a lack of voicing distinctions is not uncommon; indeed, in Australian languages it is nearly universal.

Vocal registers

Vocal registration refers to the system of vocal registers within the human voice. A register in the human voice is a particular series of tones, produced in the same vibratory pattern of the vocal folds, and possessing the same quality. Registers originate in laryngeal function. They occur because the vocal folds are capable of producing several different vibratory patterns. Each of these vibratory patterns appears within a particular range of pitches and produces certain characteristic sounds. The term register can be somewhat confusing at it encompasses several aspects of the human voice. The term register can be used to refer to any of the following

A particular part of the vocal range such as the upper, middle, or lower registers.
A resonance area such as chest voice or head voice.
A phonatory process
A certain vocal timbre
A region of the voice which is defined or delimited by vocal breaks.
A subset of a language used for a particular purpose or in a particular social setting.

In linguistics, a register language is a language which combines tone and vowel phonation into a single phonological system.

Within speech pathology the term vocal register has three constituent elements: a certain vibratory pattern of the vocal folds, a certain series of pitches, and a certain type of sound. Speech pathologists identify four vocal registers based on the physiology of laryngeal function: the vocal fry register, the modal register, the falsetto register, and the whistle register. This view is also adopted by many vocal pedagogists.

Vocal resonation

In singing, vocal resonation is a term for the process by which the basic product of phonation is enhanced in timbre and/or intensity by the air-filled cavities through which it passes on its way to the outside air. Various terms related to the resonation process include amplification, enrichment, enlargement, improvement, intensification, and prolongation, although in strictly scientific usage acoustic authorities would question most of them. The main point to be drawn from these terms by a singer or speaker is that the end result of resonation is, or should be, to make a better sound. There are seven areas that may be listed as possible vocal resonators. In sequence from the lowest within the body to the highest, these areas are the chest, the tracheal tree, the larynx itself, the pharynx, the oral cavity, the nasal cavity, and the sinuses.

References

External links

Universität Stuttgart Speech production

Wikipedia, the free encyclopedia © 2001-2006 Wikipedia contributors (Disclaimer)
This article is licensed under the GNU Free Documentation License.
Last updated on Thursday March 13, 2008 at 23:00:27 PDT (GMT -0700)
View this article at Wikipedia.org - Edit this article at Wikipedia.org - Donate to the Wikimedia Foundation