Intervals – Compound

In the unit on Intervals, we learned what intervals are, and how to determine the size and quality of an interval.

In that unit, we concentrated on the simple intervals (those in size of 1 to 8) of the major scale. But when we write the major scale, we include some other intervals – those of 9, 11, 13 :

Compound intervals

The 9, 11, and 13 intervals are compound intervals; they are intervals that are more than an octave in size. We can see this when we write a 2-octave scale.

Ninths (9)

A 9th is an interval that is an octave and a second in size. Since it is a second, it can be major, minor, diminished, and augmented in quality.

Elevenths (11)

An 11th is an interval that is an octave and a fourth in size. Since it is a fourth, it can be Perfect, diminished, or augmented in quality.

Thirteenths (13)

A 13th is an interval that is an octave and a sixth in size. Since it is a sixth, it can be Major, minor, diminished, or augmented in quality.

9, 11, and 13 in the scale

We are using a kind of shorthand in the scales to show these larger intervals. Instead of always writing a 2-octave scale, we wrap these numbers knowing that, really, the 9, 11, and 13 are an octave above what is written in the scale:

The 9, 11, and 13 intervals are marked to make thinking about extended chords easier. (More on extended chords in another unit.)