A Dictionary of Music and Musicians/Trill

TRILL (Ital. Trillo; Fr. Trille; Germ. Triller). An ornament consisting of the rapid alternation of a note with its major or minor second, generally known in English by the name of Shake, under which head it is fully described. [See vol. iii. p. 479.] The ornament itself dates from about the end of the 16th century, but it received the name of Trill at a somewhat later date, not to be exactly ascertained. It is described in the 'Nuove Musiche' of Caccini, published in Florence in 1601, under the name of Gruppo, a name which is now used to express a turn-like group of four notes, also called Groppo, thus:—

or

Caccini also makes use of the term trillo, but as indicating a pulsation or rapid repetition of a single sound sung upon a single vowel, an effect expressed in modern terminology by vibrato. [Vibrato.]

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