Voiced bilabial fricative

The voiced bilabial fricative is a type of <a href="/facts/Consonant/81X2SGS6">consonantal</a> sound, used in some <a href="/facts/Speech_communication/WEelhfTs">spoken</a> <a href="/facts/Language/IRcTok2q">languages</a>. The symbol in the <a href="/facts/International_Phonetic_Alphabet/2e7jmUaG">International Phonetic Alphabet</a> that represents this sound is ⟨β⟩, and the equivalent <a href="/facts/X-SAMPA/LEkkVBgw">X-SAMPA</a> symbol is B. The official symbol ⟨β⟩ is the <a href="/facts/Greek_alphabet/1cHwB8Dg">Greek letter</a> <a href="/facts/Beta_(letter)/oTWMRsHj">beta</a>.
This letter is also often used to represent the bilabial <a href="/facts/Approximant_consonant/SXrlw7zY">approximant</a>, though that is more precisely written with a lowering diacritic, that is ⟨β̞⟩. That sound may also be transcribed as an advanced <a href="/facts/Labiodental_approximant/wtn3Wrzu">labiodental approximant</a> ⟨ʋ̟⟩, in which case the diacritic is again frequently omitted, since no contrast is likely. It has been proposed that either a turned ⟨β⟩, reversed ⟨β⟩ or affricate ⟨βθ⟩ can be used as a dedicated symbol for the bilabial approximant, but despite occasional usage none of them have gained general acceptance. 
It is extremely rare for a language to make a phonemic contrast between the voiced bilabial fricative and the bilabial approximant. The <a href="/facts/Mapos_Buang_language/4c7Rh2vK">Mapos Buang language</a> of <a href="/facts/New_Guinea/qB0bzfSH">New Guinea</a> 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. <a href="/facts/Proto-Germanic/LJrKRx5A">Proto-Germanic</a> and <a href="/facts/Proto-Italic/JgdplDSW">Proto-Italic</a> are reconstructed as having had a contrast between the voiced bilabial fricative and the voiced labial–velar approximant /w/, albeit with [β] being an allophone for another consonant in both cases. In <a href="/facts/Bashkir_language/u1N82RGj">Bashkir language</a>, it is an intervocal allophone of /b/, and it is contrastive with /w/: балабыҙ [bɑɫɑˈβɯð] 'our child', балауыҙ [bɑɫɑˈwɯð] 'wax'.
The 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 [v].
The sound is not the primary realization of any sound in <a href="/facts/English_language/tpkxGt7b">English</a> dialects except for <a href="/facts/Chicano_English/RURuHbh1">Chicano English</a>, but it can be produced by approximating the normal English [v] between the lips; it can also sometimes occur as an allophone of /v/ after bilabial consonants.

Voiced bilabial fricative open-in-new

Voiced bilabial fricative