Aspiration
From KneeQuickie
Aspiration is the process of following a sound with a period of voicelessness, often manifesting as a strong burst of air. If the immediately following segment is syllabic, it will become partially devoiced; if it is non-syllabic, it is likely to become completely devoiced. For example, the English word "clap", phonemically /klæp/, is actually pronounced [kɬæp]: the aspiration on the /k/ devoices the /l/.
Since aspiration involves removal of voicing, it far more commonly applies to consonants that are unvoiced to begin with. In English, unvoiced plosives are allophonically aspirated when they begin a syllable; many languages, such as Ancient Greek, have a phonemic distinction between aspirated and unaspirated plosives. Fricatives and nasals may also be aspirated, although this is much rarer.
English voiceless stops are aspirated when they begin a stressed syllable (as in pen, ten, Ken), but this aspiration is not distinctive (they also have unaspirated variants in other positions, e.g. after /s/, as in spun, stun). In many languages, such as Cantonese, Hindi/Urdu, Icelandic, Korean, Mandarin, Thai and Ancient Greek, /t/ and /tʰ/ are different phonemes altogether.
Alemannic German dialects have unaspirated fortis /p t k/ as well as aspirated fortis /pʰ tʰ kʰ/; the latter series is usually viewed as clusters. Icelandic has pre-aspirated /ʰp ʰt ʰk/; some scholars interpret these as clusters. /b d g/ are normally also voiceless in Danish and most Southern varieties of German. Traditionally, they are still transcribed as <b d g>, even though what distinguishes them from their "fortis" counterparts <p t k> is mainly their lack of aspiration.
Aspiration is represented in the IPA with a superscript /h/ after a symbol (for example, /tʰ/), and in X-Sampa with the diacritic _h. In Z-Sampa, aspiration can also be written by placing the diacritic _(0 for initial partial devoicing on the following segment.
The aspiration symbol is sometimes used with voiced stops, such as dʰ. However, such "voiced aspiration", also known as breathy voice or murmur, is less ambiguously transcribed with dedicated diacritics, either d̤ or dʱ. (Some linguists restrict the former diacritic to vowels.)
