A voiced bilabial fricative is a type of consonantal sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is either a Latin or Greek-style beta, .
This letter is also often used to represent a voiced bilabial approximant, though that is more precisely written with a lowering diacritic, that is . This sound may also be transcribed as an advanced labiodental approximant , in which case the diacritic is again frequently omitted, since no contrast is likely. It has been proposed that either a turned or reversed , among others, be used as a dedicated symbol for the bilabial approximant; however, despite occasional usage, none have gained general acceptance.
It is extremely rare for a language to make a phonemic contrast between a voiced bilabial fricative and a bilabial approximant. The Mapos Buang language of New Guinea contains this contrast. Its bilabial approximant is analyzed as filling a phonological gap in the labiovelar series of the consonant system rather than the bilabial series. Proto-Germanic and Proto-Italic are reconstructed as having had a contrast between the voiced bilabial fricative and the voiced labialâÂÂvelar approximant , albeit with being an allophone for another consonant in both cases. In Bashkir language, it is an intervocal allophone of , and it is contrastive with : , .
A bilabial fricative is diachronically unstable (likely to be considerably varied between dialects of a language that makes use of it) and is likely to shift to .
The sound is not the primary realization of any sound in English dialects except for Chicano English, but it can be produced by approximating the normal English between the lips; it can also sometimes occur as an allophone of after bilabial consonants.
Features of a voiced bilabial fricative: