to vary (one's voice, etc) in tone, pitch, etc

to keep (something) in proper measure or proportion; to temper or regulate (something)

to vary the amplitude, frequency, or phase of (a waveone of two combined waves) to match the variations of another the other, esp in combining a radio wave with a the sound or vision signal it carries

in music, to pass by regular chord or melodic progression from one key or tonality into another