Phoneticians define phonation as "use of the laryngeal system to generate 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."
[image] A voiced sound is produced when an overpressure of air in 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 folds. The vowels are usually voiced, but there are also voiced consonants.
If the vocal folds do not vibrate, then the sound (usually a Consonant) is called voiceless.
Other sounds may be produced by completely blocking off the airstream and then releasing the folds. The sound of this type produced at the glottis is called a glottal stop.
The voice source is used to change intonation and the tone of words by varying the subglottal pressure as well as the tension of the vocal folds. This leads to changes in the frequency of vibration, which are in turn perceived by the listener as modifications in pitch and/or in loudness. During speech the flow of air is relatively small because of constrictions of the folds.
Subglottal pressure is regulated by a number of factors, namely: the respiratory muscles, gravity and elasticity.
At the other extreme, a fully closed glottis allows no air to pass; with no airflow, there is no vocal cord vibration. This is simply called glottal closure, and when unaccompanied by a Place of articulation in the vocal tract, is a Glottal stop.
Often a language will utilize some point of this continuum other than its mid or end points. For example, Gujarati has vowels with a half-lax phonation called breathy or murmured, and Burmese has vowels with a half-tense phonation called creaky 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:
| Mazatec | translation | |
| modal voice | [já] | tree |
| breathy voice | [ja̤] | he wears |
| creaky voice | [ja̰] | he carries |
Note:
There are other possibilities, and any division is arbitrary. The IPA diacritics under-ring and subscript wedge, commonly called "voiceless" and "voiced", are sometimes used to indicate more lax/open and tense/closed states of the glottis, respectively. (Ironically, adding the 'voiced' diacritic to the symbol for a voiced consonant indicates less modal voicing, not more, because a modally voiced sound is already fully voiced, and any further tension in the vocal cords dampens their vibration.) A phonation intermediate between modal and breathy is called lax, while one intermediate between modal and creaky is called stiff.
A series of seven alveolar plosives, with phonations ranging from an open/lax to a closed/tense glottis, are:
It has long been noted that, phonologically and historically, the glottal consonants, , do not behave like other consonants. Phonetically, they have no manner or Place of articulation other than their phonation (that is, glottal closure, breathy voice, and open airstream). Some phoneticians have described them as neither glottal nor consonantal, but instances of pure phonation.
Certain English morphemes have both voiced and voiceless allomorphs, e.g. the ending -s (voiced in kids but voiceless in kits ) or the past tense ending -ed (voiced in buzzed but voiceless in fished .
In languages such as French, all obstruents occur in pairs of a voiced one and an unvoiced one.
Mandarin Chinese has pairs of aspirated and unaspirated voiceless plosives and aspiration is the main distinction rather than phonation.
A few languages, such as Finnish or Alemannic, have no voiced obstruents but pairs of long and short consonants instead.