A scale that interests all composers and arrangers
This may be the most fasinating of all altered scales. It actually belongs in two places, since octatonic I is for X7 chords, but octatonic II works better with non-dominant chords, and it clearly contains a minor chord – 1 b3 5.Going only by the form there are only three scales, but we do not hear them that way. We hear each as its own thing, it’s own universe. And octatonic I and II, while having a vexingly similar sound, don’t fit in the same places. Spelling is variable, according to ease of reading and common sense.
You are unlike to find either version of this scale in Bach, but by the middle of the 1800s it was common, and it has been used ever since. Today it is all over the place, in all kinds of traditional styles, and it is very common in jazz. There are only minor differences between octatonic and the jazz “alt dominant” scale.