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(April 2008)| The bilabial trill is a type of consonantal sound,
used in some spoken languages. The symbol in the International
Phonetic Alphabet that represents this sound is ⟨ʙ⟩, and the
equivalent X-SAMPA symbol is B\. In many of the languages where
the bilabial trill occurs, it only occurs as part of a
prenasalized bilabial stop with trilled release, [mbʙ]. This
developed historically from a prenasalized stop before a
relatively high back vowel, such as [mbu]. In such instances,
these sounds are usually still limited to the environment of a
following [u]. There is also a very rare voiceless alveolar
bilabially trilled affricate, [t̪͡ʙ̥] (occasionally written
"tᵖ") reported from Pirahã and from a few words in the
Chapacuran languages Wari’ and Oro Win. The sound also appears
as an allophone of the labialized voiceless alveolar stop /tʷ/
of Abkhaz and Ubykh, but in those languages it is more often
realised by a doubly articulated stop [t͡p]. In the