(1):
(n.) Sound modulated; melody.
(2):
(n.) A change of key, whether transient, or until the music becomes established in the new key; a shifting of the tonality of a piece, so that the harmonies all center upon a new keynote or tonic; the art of transition out of the original key into one nearly related, and so on, it may be, by successive changes, into a key quite remote. There are also sudden and unprepared modulations.
(3):
(n.) The act of modulating, or the state of being modulated; as, the modulation of the voice.