*N.B* Prior theory knowledge will be extremely useful to get anything out of this article. That being said, these are just a few thoughts on the scale in general and a few possibilities on how to use it, but the possibilities are endless. I really hope you like the article and can take something useful away from it. Enjoy!
The octatonic scale poses as an interesting anomaly in the realm of musical scales. Like the Wholetone scale, it is symmetrical, and aptly named. While being named for the eight pitches that make up the scale, each note could be treated as the tonic' of the scale because of it symmetry. Given the way the scale is arranged, several effects may be achieved through its use, especially when switching tonalities or parallel chords.
Two' octatonic scales can be formed depending on where one starts in the scale. Being a repeating pattern of W-H, or H-W, there can only be 6 H-W and 6 W-H scales, or 3 scales overall when you see the W-H and H-W variants as deriving from one set of pitches. The H-W scales are most idiomatically used over dominant seventh chords (e.g. G7), which bring out altered' tones, while the W-H scales are mostly used for playing over diminished harmony (e.g. F#dim7). For example, The W-H octatonic scale is C-D-Eb-F-Gb-Ab-A-B-C, and the D H-W scale is D-Eb-F-Gb-Ab-A-B-C-D. The two scales use the same set of notes. The scale can also be viewed as a collection of two Diminished seventh chords, of which there are only 3 uniquely defined under the 12-tone system. Take 3C2 =(3*2)/(2*1)=3, which is exactly how many unique octatonic scales there are. Therefore, by choosing two diminished seventh chords, one immediately forms and octatonic scale.
Besides the immediate recognition that one can form diminished chords from this scale, another interesting thing to note in the scale is that one can form four distinct major and minor triads when looking at the scale. The notes that are situated after the whole steps (B, D, F, Ab in the given example) has associated with it both a major and minor triad with the given notes as roots (note how these notes form diminished seventh chords as above). The most intriguing aspect of this is that the cycle from BM-Bm-DM-Dm- Forms parallel and relative relations. Bm is the parallel minor of BM, and is likewise the relative minor of DM. This relationship may be useful if one would like to capture outside' sounds while transitioning from a Major to relative or parallel minor. Worth noting diatonically is the fact that a dominant seventh chord can be built on these same notes, relating dominant seventh chords that are a minor third apart from each other.
Substituting these seventh chords for each other can give interesting results, as they can be viewed as containing extensions and or alterations the Dominant seventh chords they are substituting for. Therefore one can theoretically shift from keys related by minor thirds in this way, by treating the chord used to substitute as the V7 in the new key. Connecting this is the idea of the whole tone scale, where an altered dominant is created on every note, one can theoretically ascend or descend chromatically through all twelve tones by altering the use of the whole tone and octatonic scales over ascending or descending Dominant chords, which can be viewed as a string of triton substitutions. Other interesting uses may be major or minor chords in succession related by minor thirds.
Perhaps one of the most interesting uses of the scale is over the iv chord borrowed from parallel minor in a major key. Because the octatonic scale accommodates both chords, one can play the scale over the chord (eg C H-W over the CM-Cm chords in the following progression: G-G7-C-Cm). One may also try the G H-W scale over the G7 chord as it brings out the altered tones of the seventh chord (which then connects two H-W scales to each other by relation of a fifth, just like how typical chords in a circle progression are related).
Surely the octatonic scale has limitless potential; it is all in the manner by which one chooses to apply it. Given here are only a few ideas about relations and possible uses, but the possibilities are endless.
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