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.

• The process of applying a signal to a carrier, modulating.
  
• Methods of modulating.