\Mod`u*la"tion\, n. [L. modulatio: cf. F.
modulation.]
1. The act of modulating, or the state of being modulated;
   as, the modulation of the voice.
2. Sound modulated; melody. [R.] --Thomson.
3. (Mus.) 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.