percussive consonant

In phonetics, the airstream mechanism is the method by which airflow is created in the vocal tract. Along with phonation and articulation, it is one of three main components of speech production. The airstream mechanism is mandatory for sound production and constitutes the first part of this process, which is called initiation.

The organ generating the airstream is called the ''initiator'' and there are three initiators used in spoken human languages:
* the diaphragm together with the ribs and lungs ''(pulmonic'' mechanisms),
* the glottis ''(glottalic'' mechanisms), and
* the tongue ''(lingual'' or ''"velaric"'' mechanisms).

Though not used in any language, the cheeks may be used to generate the airstream ''(buccal'' mechanism, notated in VoQS). See buccal speech.

After a laryngectomy, the esophagus may be used as the initiator (notated for simple esophageal speech and for tracheo-esophageal speech in VoQS). See esophageal speech.

''Percussive'' consonants are produced without any airstream mechanism.

Types of airstream mechanism

Any of the three initiators − diaphragm, glottis or tongue − may act by either increasing or decreasing the pressure generating the airstream. These changes in pressure often correspond to outward and inward airflow, and are therefore termed ''egressive'' and '' ingressive'' respectively.

Of these six resulting airstream mechanisms, four are found lexically around the world:
* ''pulmonic egressive,'' where the air is pushed out of the lungs by the ribs and diaphragm. All human languages employ such sounds (such as vowels), and nearly three out of four use them exclusively.
* '' glottalic egressive,'' where the air column is compressed as the glottis moves upward. Such consonants are called ejectives. Ejective and ejective-like consonants occur in 16% of the languages.
* ''glottalic ingressive,'' where the air column is rarefied as the glottis moves downward. Such consonants are called implosives. Implosive and implosive-like consonants occur in 13% of the world's languages. Despite the name, the airstream may not actually flow inward: While the glottis moves downward, pulmonic air passes outward through it, but the reduction in pressure makes an audible difference to the sound.
* ''lingual ingressive,'' AKA ''velaric ingressive,'' where the air in the mouth is rarefied by a downward movement of the tongue. These are the click consonants. Clicks are regular sounds in ordinary words in fewer than 2% of the world's languages, all in Africa.

These mechanisms may be combined into airstream contours, such as clicks which release into ejectives.

The Khoisan languages have pulmonic, ejective, and click consonants, the Chadic languages have pulmonic, implosive, and ejective consonants, and the Nguni languages utilize all four, pulmonic, click, implosive, and ejective, in normal vocabulary. Most other languages utilize only one or two airstream mechanisms.

In interjections, the other two mechanisms may be employed. For example, in countries as diverse as Sweden, Turkey, and Togo, a pulmonic ingressive ("gasped" or "inhaled") vowel is used for back-channeling or to express agreement, and in France a lingual egressive (a "spurt") is used to express dismissal. The only language where such sounds are known to be contrastive in normal vocabulary is the extinct ritual language Damin (also the only language outside Africa with clicks); however, Damin appears to have been intentionally designed to differ from normal speech.

Pulmonic initiation

Initiation by means of the lungs (actually the diaphragm and ribs) is called pulmonic initiation. The vast majority of sounds used in human languages are pulmonic egressives. In most languages, including all the languages of Europe (excluding the Caucasus), all phonemes are pulmonic egressives.

The only attested use of a phonemic pulmonic ingressive is a lateral fricative in Damin, a ritual language formerly used by speakers of Lardil in Australia. This can be written with the extended version of the International Phonetic Alphabet as . !Xóõ has ingression as a phonetic detail in one series of its clicks, which are ''ingressive voiceless nasals with delayed aspiration'', . Peter Ladefoged considers these to be among the most difficult sounds in the world. Other languages, for example in Taiwan, have been claimed to have pulmonic ingressives, but these claims have either proven to be spurious or to be occasional phonetic detail.

In interjections, but not in normal words, pulmonic ingressive vowels or words occur on all continents. This is commonly done for back-channeling (as with in Ewe) or affirmation (as with in Swedish). In English, an audible intake of breath, , or an indrawn consonant such as or is used in a conversation to indicate that someone is about to speak or is preparing to continue speaking. In some languages, such as Finnish and Amharic, entire phrases may be uttered with an ingressive airstream. (See ingressive sound.)

Glottalic initiation

It is possible to initiate airflow in the upper vocal tract by means of the vocal cords or glottis. This is known as glottalic initiation.

For egressive glottalic initiation, one lowers the glottis (as if to sing a low note), closes it as for a glottal stop