Ditone

The interval consisting of two consecutive 9/8 whole tones.

It has the ratio 81/64 (408 cents) and is also called the Pythagorean Major Third.

[from John Chalmers, Divisions of the Tetrachord]

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Below is a diagram illustrating this description, on an approximate logarithmic scale. The ditone in this tetrachord occurs between "A" and "F".

                    ratio      vector
                                 2  3

                /  A  1/1  -+- [ 0  0]   
               /            |            \
9/8  [-3  2] = tone         |             \
               \            |              \
               /\  G  9/8  -+- [-3  2]      81/64   [-6  4]  =  ditone
              /             |              /
9/8  [-3  2] = tone         |             /
              \             |            /
               \   F 81/64 -+- [-6  4]   \
                            |              256/243  [ 8 -5]  =  limma
                   E  4/3  -+- [ 2 -1]   /

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