Voiceless consonants are produced with the
vocal folds open (spread) and not vibrating, and voiced consonants are produced when the vocal folds are fractionally closed and vibrating (
modal voice). Voiceless aspiration occurs when the vocal folds remain open after a consonant is released. An easy way to measure this is by noting the consonant's
voice onset time, as the voicing of a following vowel cannot begin until the vocal folds close. In some languages, such as
Navajo, aspiration of stops tends to be phonetically realised as voiceless velar airflow; aspiration of affricates is realised as an extended length of the frication. Aspirated consonants are not always followed by vowels or other voiced sounds. For example, in
Eastern Armenian, aspiration is contrastive even word-finally, and aspirated consonants occur in
consonant clusters. In
Wahgi, consonants are aspirated only when they are in final position. Kurukh distinguishes /Ch, Cʰ, Cʰh/ with occasional minimal pairs like /dʱandha:/ "astonishment" and /dʱandʱa:/ "exertion". Clusters of voiced aspirates and /h/ are possible too as in /madʒʱhi:/ "middle" and /madʒʱis/ "zamindar's agent".
Degree The degree of aspiration varies: the voice onset time of aspirated stops is longer or shorter depending on the language or the place of articulation. Armenian and
Cantonese have aspiration that lasts about as long as English aspirated stops, in addition to unaspirated stops. Korean has lightly aspirated stops that fall between the Armenian and Cantonese unaspirated and aspirated stops as well as strongly aspirated stops whose aspiration lasts longer than that of Armenian or Cantonese. Aspiration varies with
place of articulation. The Spanish voiceless stops have
voice onset times (VOTs) of about 5, 10, and 30 milliseconds, and English aspirated have VOTs of about 60, 70, and 80 ms. Voice onset time in Korean has been measured at 20, 25, and 50 ms for and 90, 95, and 125 for .
Doubling {{listen When aspirated consonants are doubled or
geminated, the stop is held longer and then has an aspirated release. An aspirated affricate consists of a stop, fricative, and aspirated release. A doubled aspirated affricate has a longer hold in the stop portion and then has a release consisting of the fricative and aspiration.
Preaspiration Icelandic and
Faroese have consonants with
preaspiration , and some scholars interpret them as consonant clusters as well. In Icelandic, preaspirated stops
contrast with double stops and single stops: Preaspiration is also a feature of
Scottish Gaelic: Preaspirated stops also occur in most
Sami languages. For example, in
Northern Sami, the unvoiced stop and affricate phonemes , , , , are pronounced preaspirated (, , , ) in medial or final position. Further,
Proto-Siouan is notable for contrasting aspirated stops with preaspirated stops.
Fricatives and sonorants Although most aspirated obstruents in the world's languages are stops and affricates,
aspirated fricatives such as , and have been documented in
Korean and
Xuanzhou Wu, and has been described for Spanish, though these are allophones of other phonemes. Similarly, aspirated fricatives and even aspirated nasals, approximants, and trills occur in a few
Tibeto-Burman languages, some
Oto-Manguean languages, the
Hmongic language
Hmu, the
Siouan language
Ofo, and the
Chumashan languages
Barbareño and
Ventureño. Some languages, such as
Choni Tibetan, have as many as four contrastive aspirated fricatives , and .
Voiced consonants with voiceless aspiration True aspirated voiced consonants, as opposed to
murmured (breathy-voice) consonants such as the that are common among the
languages of South Asia, are extremely rare. They have been documented in
Kelabit. ==Phonology==