Voiced bilabial fricative

The 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 β, and the equivalent X-SAMPA symbol is B. The official symbol β is the Greek letter beta, though on the IPA chart the Latin beta is used.

Voiced bilabial fricative
IPA Number127
Entity (decimal)βꞵ
Unicode (hex)U+03B2U+A7B5
Audio sample
Voiced bilabial approximant
Audio sample

This letter is also often used to represent the bilabial approximant, though that is more precisely written with a lowering diacritic, that is β̞. That sound may also be transcribed as an advanced labiodental approximant ʋ̟, in which case the diacritic is again frequently omitted, since no contrast is likely.[1][2] It has been proposed that either a turned ⟨β⟩ or reversed ⟨β⟩ be used as a dedicated symbol for the bilabial approximant, but despite occasional usage this has not gained general acceptance.[3]

It is extremely rare for a language to make a phonemic contrast between the voiced bilabial fricative and the 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.[4]

The bilabial fricative is diachronically unstable[clarify] and is likely to shift to [v].[5]

The sound is not used in English dialects except for Chicano English, but it can be produced by approximating the normal English [v] between the lips.