The voiced bilabial fricative is a type of consonantal sound, used in some spokenlanguages. The symbol in the International Phonetic Alphabet that represents this sound is ⟨β⟩ (or more properly ⟨ꞵ⟩), and the equivalent X-SAMPA symbol is ⟨B⟩. The symbol ⟨β⟩ is the Greek letterbeta. This symbol is also sometimes used to represent the bilabial approximant, though that is more clearly written with the lowering diacritic, that is ⟨β̞⟩. Theoretically, it could also be transcribed as an advanced labiodental approximant⟨ʋ̟⟩, but this symbol is hardly (if ever) used in this manner. Very few languages are known to make a phonemic contrast between the voiced bilabial fricative and the bilabial approximant, but one language that does make this contrast is the Tarahumara language of the Uto-Aztecan family. The bilabial fricative is diachronically unstable and is likely to shift to [v]. In the English language, this sound is not used, but can be made by approximating the normal "v" sound between the two lips.
^Phonetic studies such as Quilis (1981) have found that Spanish voiced stops may surface as spirants with various degrees of constriction. These allophones are not limited to regular fricative articulations, but range from articulations that involve a near complete oral closure to articulations involving a degree of aperture quite close to vocalization
Hayward, Katrina; Hayward, Richard J. (1999), "Amharic", Handbook of the International Phonetic Association: A guide to the use of the International Phonetic Alphabet, Cambridge: Cambridge University Press, pp. 45–50, doi:10.1017/S0025100300004874, ISBN0-521-65236-7