Definitions of modulate:

• verb:   vary the frequency, amplitude, phase, or other characteristic of (electromagnetic waves)
• verb:   adjust the pitch, tone, or volume of
• verb:   change the key of, in music

  Example: "Modulate the melody"

• verb:   fix or adjust the time, amount, degree, or rate of

  Example: "Modulate the pitch"

• verb:   of one's speech, varying the pitch