By being made superscript, any IPA letter may function as a diacritic, conferring elements of its articulation to the base letter . ( See secondary articulation for a list of superscript IPA letters supported by Unicode . ) Those superscript letters listed below are specifically provided for by the IPA; others include } } ( with fricative release ), } } ( with affricate onset ), } } ( prenasalized ), } } ( with breathy voice ), } } ( glottalized ), } } ( with a flavor of ), } } ( with compressed ).
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However, laboratory measurements have never succeeded in demonstrating simultaneous frication at two points of articulation, and such sounds turn out to be either secondary articulation, or a sequence of two non-simultaneous fricatives . ( Despite its name, the " voiceless labial-velar fricative " is actually a voiceless approximant; the name is a historical remnant from before the distinction was made . ) Such sounds can be made, with effort, but it is very difficult for a listener to discern them, and therefore they are not expected to be found as distinctive sounds in any language.
