Simple and compound intervals · Inversion and consonance · Music theory
A simple interval fits within an octave; a compound one goes beyond it. A compound interval is named by its number (9th, 10th, 12th) or as the simple one…
Simple and compound intervals
A simple interval fits within an octave; a compound one goes beyond it. A compound interval is named by its number (9th, 10th, 12th) or as the simple one plus an octave. To go from one to the other, add or subtract 7: a 10th is a 3rd plus an octave, and two octaves make a 15th.
The quality is that of the simple interval: C4–E5 is a major 10th because C–E is a major 3rd.
Compound intervals in harmony
A compound interval sounds very like its simple form, and in harmony it is usually treated the same: a 10th is an imperfect consonance like the 3rd. The exception is the 9th, which keeps its own name because it forms chords different from those with a 2nd.
In four-part writing, 10ths and 12ths between bass and tenor are normal, because the bass usually sits far below: the distance that really matters is the one between the upper voices.