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In linguistics, voicelessness is the property of sounds being pronounced without the larynx vibrating. Phonologically, this is a type of phonation, which contrasts with other states of the larynx, but some object that the word "phonation" implies voicing, and that voicelessness is the lack of phonation.
The International Phonetic Alphabet has distinct letters for many voiceless and modally voiced pairs of consonants (the obstruents), such as [p b], [t d], [k ɡ], [q ɢ] [f v], [s z]. In addition, there are diacritics for voicelessness, ⟨ ̥ ⟩ (U+0325 ̥ combining ring below) and ⟨ ̊ ⟩ (U+030A ̊ combining ring above), which is used for letters with a descender. Diacritics are typically used with letters for prototypically voiced sounds, such as vowels and sonorant consonants: [ḁ], [l̥], [ŋ̊].
Voiceless vowels and other sonorants 
Sonorants are those sounds, such as vowels and nasals, which are voiced in most of the world's languages. However, in some languages sonorants may be voiceless, usually allophonically. For example, the Japanese word sukiyaki is pronounced [su̥kijaki]. This may sound like [skijaki] to an English speaker, but the lips can be seen compressing for the [u̥]. Something similar happens in English with words like peculiar [pʰə̥ˈkjuːliɚ] and potato [pʰə̥ˈteɪtoʊ].
Sonorants may also be contrastively voiceless, not just voiceless due to their environment. Standard Tibetan, for example, has a voiceless /l̥/ in Lhasa, which sounds similar to, but is not as noisy as, the voiceless lateral fricative /ɬ/ in Welsh, and which contrasts with a modally voiced /l/. Welsh contrasts several voiceless sonorants: /m, m̥/, /n, n̥/, /ŋ, ŋ̊/, and /r, r̥/, the latter represented by "rh".
In the Moksha language there is even a voiceless palatal approximant /j̊/ (written in Cyrillic as <йх> jh) along with /l̥/ and /r̥/ (written as <лх> lh and <рх> rh). The last two have also palatalized counterparts /lʲ̥/ and /rʲ̥/ (<льх> and <рьх>). In the Kildin Sami language there is also this /j̊/ <ҋ>.
On the other hand, although contrastively voiceless vowels have been reported several times, they have never been verified (L&M 1996:315).
Lack of voicing contrast in obstruents 
Many languages lack a distinction between voiced and voiceless obstruents (stops, affricates, and fricatives). This is nearly universal in Dravidian languages and Australian languages, but is widely found elsewhere, for example in Mandarin Chinese, Korean, Finnish, and the Polynesian languages. Consider Hawaiian, which has a /p/ and /k/, but no /b/ or /ɡ/. In many such languages, obstruents are realized as voiced in voiced environments, such as between vowels or between a vowel and a nasal, and voiceless elsewhere, such as at the beginning or end of the word or next to another obstruent. This is the case for example for Dravidian, Australian, and Korean, but not in Mandarin or Polynesian. Usually these variable sounds are transcribed with the voiceless IPA letters, though in Australia the letters for voiced consonants are sometimes used.
It appears that voicelessness is not a single phenomenon in such languages. In some, such as the Polynesian languages, the vocal cords are required to actively open to allow an unimpeded (silent) airstream. This is sometimes called a breathed (/ˈbrɛθt/) phonation (not to be confused with breathy voice). In others, such as many Australian languages, voicing ceases during the hold of a stop (few Australian languages have any other kind of obstruent) because airflow is insufficient to sustain it, and if the vocal cords open this is due to passive relaxation. Correspondingly, Polynesian stops are reported to be held for longer than Australian stops, and are seldom voiced, whereas Australian stops are prone to having voiced variants (L&M 1996:53), and are often represented as having no phonemically voiceless consonants at all. In Southeast Asia, when stops occur at the end of a word they are voiceless because the glottis is closed, not open, and so these are said to be unphonated (have no phonation) by some phoneticians who considered "breathed" voicelessness to be a phonation.
- The International Phonetic Alphabet in Unicode, UCL Division of Psychology & Language Sciences
- Jerold Edmondson, John Esling, Jimmy Harris, and James Wei, "A phonetic study of the Sui consonants and tones" Mon–Khmer Studies 34:47–66
- R. M. W. Dixon. (1977). A Grammar of Yidiny. Cambridge: Cambridge University Press.
General references 
- Ladefoged, Peter; Maddieson, Ian (1996). The Sounds of the World's Languages. Oxford: Blackwell. ISBN 0-631-19814-8.