The Collaborative International Dictionary of English v.0.48:

Modulate \Mod"u*late\, v. t. [imp. & p. p. Modulated; p. pr. &
   vb. n. Modulating.] [L. modulatus, p. p. of modulari to
   measure, to modulate, fr. modulus a small measure, meter,
   melody, dim. of modus. See Mode.]
   1. To form, as sound, to a certain key, or to a certain
      portion.
      [1913 Webster]

   2. To vary or inflect in a natural, customary, or musical
      manner; as, the organs of speech modulate the voice in
      reading or speaking.
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            Could any person so modulate her voice as to deceive
            so many?                              --Broome.
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   3. (Electronics) To alter the amplitude, frequency, phase, or
      intensity of (the carrier wave of a radio signal) at
      intervals, so as to represent information to be conveyed
      by the signal; -- a technique used to convey information
      by means of radio waves transmitted by one electronic
      device and received by another.
      [WordNet 1.5]