These are a group of seven note (hence heptatonic) scales consisting 5 whole steps and 2 half steps, in which the half steps are maximally separated.
The term “diatonic” means “ (progressing) through tones.” These the most common scales encountered in traditional music as well as certain modern genres. The diatonic scale is referred to as Heptatonia Pirma. The notes of these diatonic scales are often sung using the solfege syllables (do-re-me-fa-sol-la-ti).
Elaboration on the Construction:
The half steps are required to be maximally separated in the scale, when played through either one or multiple octaves. This can only be achieved by placing the half steps after every two to three (or four) whole steps. This gives the familiar shape of all the common major and minor scales.
If we take the example of the major scale below and extend it for a few (here three) octaves, the placement of the steps becomes obvious:
2-2-1-2-2-2-1~2-2-1-2-2-2-1~2-2-1-2-2-2-1 (extended to 3 octaves, Major Scale)
The half notes occur after every two or three notes, thus keeping them maximally separated. This separation is required as, two closely placed half notes do not sound as good as the scales where they are maximally spaced. Read more....
Analyzing the other scales ("extended") mentioned below, we see –
Natural Minor: 2-1-2-2-1-2-2~2-1-2-2-1-2-2~2-1-2-2-1-2-2
Harmonic Minor: 2-1-2-2-1-3-1~2-1-2-2-1-3-1~2-1-2-2-1-3-1 (aka the "Mohammedan scale")
Ascending Melodic Minor: 2-1-2-2-2-2-1~2-1-2-2-2-2-1~2-1-2-2-2-2-1
Descending Melodic Minor: 2-2-1-2-2-1-2~2-2-1-2-2-1-2~2-2-1-2-2-1-2
Thus all of them have at least two (upto four) whole steps separating the half steps.
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