Alveolar trill

The alveolar trill is a type of consonantal sound, The symbol in the International Phonetic Alphabet that represents dental, alveolar, and postalveolar trills is [r].

In the majority of Indo-European languages, this sound is at least occasionally allophonic with an alveolar tap [ɾ], particularly in unstressed positions. Exceptions to this include Spanish, and Portuguese which treat them as separate phonemes.

Features of the alveolar trill:

Its manner of articulation is trill, which means it is produced by vibrations of the tongue against the place of articulation.

在一些語言, 例如捷克語, 齒齦顫音可以作為成節輔音 , 例如捷克語 krk (頸).

多數漢語中的方言都沒有此音。但湖北的中北部的一部分中原官話區和西南官話區里，即當陽、江陵，鍾祥、京山一帶，直至神農架北部地區，存在有顫音/r/。而且此種顫音/r/，多半是由詞尾「子」演變而來。另外，某些普通話或官話方言的民歌如鳳陽花鼓裡，歌詞「得兒叮噹飄一飄」裡，如果讀時舌肌放鬆，就會讀出清齒齦顫音。

from http://en.wikipedia.org/wiki/Alveolar_trill