trem·o·lo /ˈtrɛməˌlo/
  顫音;顫聲;風琴顫音裝置
  Tre·mo·lo n.  Mus. (a) The rapid reiteration of tones without any apparent cessation, so as to produce a tremulous effect. (b) A certain contrivance in an organ, which causes the notes to sound with rapid pulses or beats, producing a tremulous effect; -- called also tremolant, and tremulant.
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  tremolo
       n 1: (music) a tremulous effect produced by rapid repetition of a
            single tone or rapid alternation of two tones
       2: vocal vibrato especially an excessive or poorly controlled
          one