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. 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. (See voice onset time.) 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 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. Fricatives and sonorants Although most aspirated obstruents in the world's languages are stops and affricates, aspirated fricatives such as , or have been documented in Korean, though these are allophones of other phonemes. Similarly, aspirated fricatives and even aspirated nasals, approximants, and trills occur in a few Tibeto-Burman languages, in some Oto-Manguean languages, in the Hmongic language Hmu,