Compound intervals (beyond the octave)
Music theory · Intervals · Level 4 · 7 min
An interval larger than an octave is called a compound interval. You name it by carrying on counting: ninth, tenth, eleventh, twelfth, thirteenth, and two octaves = fifteenth.
| Compound interval | = simple interval + octave |
|---|---|
| 9th | second |
| 10th | third |
| 11th | fourth |
| 12th | fifth |
| 13th | sixth |
Rule: to reduce a compound interval, subtract 7 (not 8!): 10 − 7 = 3 (a third). The quality doesn't change: a minor 9th = minor 2nd + octave.
M:4/4 L:1/4 Q:1/4=72 K:C "^9th"[Cd]2 "^10th"[Ce]2 | "^11th"[Cf]2 "^12th"[Cg]2 | "^13th"[Ca]2 "^15th"[Cc']2 |]
Where do you meet them?
- In extended jazz chords: 9ths, 11ths and 13ths are notes added above a seventh chord (C9, F13…). Part two of this course covers them in detail.
- In the pianist's left hand: the tenth (C to the E an octave higher) makes a rich, singing bass, typical of stride piano and Chopin. It needs a big hand: you can roll it (a quick arpeggio).
- In four-part writing: the gap between tenor and bass may exceed an octave.
Test your hand: put your thumb on C and reach for the E of the next octave with your fifth finger. If you reach it without strain you can play tenths; otherwise roll them — even Rachmaninoff rolled some thirteenths… although he could reach a great many!