The Voicing reference article from the English Wikipedia on 24-Apr-2004
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Voicing

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In phonetics, the term voice refers to a certain vibrating quality in the phonation of consonants - both fricatives and stops.

For example: in conventional English pronunciation, the sound represented by "t" has a voiced equivalent: "d".

Voiceless/voiced pairs include:

p and b
k and g
f and v
s and z
t and d

Other pairings appear with consonantal clusters or in other languages.

Preceived presence or absence of voice can serve as a phonemic marker.

See also