The Just Scales
The Just Scale is built to maximise the number of consonant intervals that have
exact frequency ratios. The major triad, ratios 4/5/6 is the starting
place. One of the features that makes the Just Scale so attractive in the West
is that most of Western harmony is built around this triad.
Step 1: Form a major triad:
Step 2: Form major triads from the top and bottom notes of this triad:
Step 3: Bring the ratios from step 2 within the range of a single octave:
Step 4: Arrange notes in ascending order:
This is known as the Just diatonic scale. Examining the intervals between each
step,
Discussion
There are two whole tones: 9/8 = 1.125 called the major tone, and 10/9 =
1.1'called the minor tone. The semitone has a ratio of 16/15 = 1.06'. The minor
third between notes 2 and 4, (4/3)/(9/8) = 32/27 = 1.'185' , does not have the
desired ratio of 6/5 = 1.2. The perfect 5th between notes 2 and 6, (10/6)/(9/8)
= 40/27 = 1.'481' does not have the desired ratio 3/2 = 1.5.