mod·u·late 
(mŏjə-lāt′)
(mŏjə-lāt′)v. mod·u·lat·ed, mod·u·lat·ing, mod·u·lates
v.tr.
1. To regulate or adjust to a certain degree: physiological mechanisms that modulate the body's metabolic rate.
2. To change or vary the pitch, intensity, or tone of (one's voice or a musical instrument, for example).
3. Electronics
a. To vary the frequency, amplitude, phase, or other characteristic of (electromagnetic waves).
b. To vary (electron velocity) in an electron beam.
4. Biochemistry To act on (a receptor, for example) as an activator, an inhibitor, or both.
v.intr.
Music
Music
To move from one key or tonality to another by means of a melody or chord progression.
[Latin modulārī, modulāt-, to measure off, to regulate, from modulus, diminutive of modus, measure; see med- in the Appendix of Indo-European roots.]
mod′u·la·bili·ty n.
modu·la′tive, modu·la·to′ry (-lə-tôr′ē) adj.