In addition to what Jolly wrote, I would like to say this:
Pitch Axis is used to construct chord progressions. Basically you take a pitch and you make it the “home pitch”, and choose the scales according to the chords that are being played in the backing.
For example let’s say that we decided to use C as the pitch.

You can play a simple chord progression like this :
Cmaj/ Cm/ C7

The scales that you can play are: C major, C minor, C mixolydian
Or……………………………….................C Lydian, C dorian, C mixolydian



Keys you went thru…C, Cm, F
……………………..........G, Bb, F

Pitch axis is a powerful tool for Direct Modulation and Modal Interchange.
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