# Second and seventh

Audio: second and seventh (0:08)

second and seventh plays Pythagorean seconds and sevenths on a piano. The second and seventh figure shows the score consists of the following:

• Bar 1 contains an interval of a major second, DE.
• Bar 2 contains an interval of a minor seventh, DC.
• Bars 3-4 contain a melody consisting of the intervals of unison and octave, fourth and fifth, and second and seventh.

The Pythagorean major second has a frequency ratio of 9:8. Its inverse, the minor seventh, has a ratio of 16:9.

The major second is an interval of a fifth above the fifth. To construct it using Pythagorean tuning, multiply the frequency ratio of a fifth, 3:2, by itself to get 9:4, then half it to get 9:8, the octave below, which is an interval of a major second. The inverse of 9:8 is 8:9, the octave above is 16:9, and that produces the interval of a major seventh.

Pythagorean tuning has now produced a third pair of intervals: a major second and a minor seventh with frequency ratios 9:8 and 16:9 respectively.