Prevoicing, in phonetics, is voicing before the onset of a consonant or beginning with the onset of the consonant but ending before its release. In the extensions to the International Phonetic Alphabet for speech pathology, prevoicing is transcribed with a voicing diacritic ( ?, U+032C) placed in front of the consonant, as in [ ?d].
In several Khoisan languages of Southern Africa, such as Taa and !Kung, stops such as /dz?/ ([ds?] or [dts?]) and /dz'/ ([ds'] or [dts']) are sometimes analyzed as being prevoiced / ?ts?/ and / ?ts'/, though the cessation of voicing has also been analyzed as phonetic detail in the transition of a phonemically voiced consonant to its voiceless aspiration or ejection. (See aspirated voiced consonant and voiced ejective.)
Kelabit has a similar set of aspirated voiced consonants. Not all speakers produce the aspiration, resulting in prevoiced (or mixed voiced) [b?p, d?t, k] (or equivalently [ ?p, ?t, ?k], and neighboring Lun Dayeh has [b?p, d?t?, k] (= [ ?p, ?t?, ?k].