[1] Procedures of contrast include stratification, juxtaposition, and interpolation.
Procedures of connection include gradation, amalgamation, and dissolution.
Harmonic contrast means to have a change in keys or chords or even cadences.
Contrast is not only a way of adding interest, and difference in a song, but is essential to the aesthetic illusion of dramatic resolution of conflict.
[2] Contrast is a sector that provides a sub-conscious break to absorb the material from the main expository piece.