Originally Posted by Gordon Scott
This has been puzzling me a bit ... it's not a scale with which I'm familiar, but I would have considered it to contain the natural fourth and the flat fifth, not the sharp 4th, so G, A, B, C, Db, E, F#.
My personal view is that it's not a Lydian variant, which contains the sharp 4th, not the natural fourth.

I'm no expert, though, so maybe AI outranks me here?

I agree, Gordon. In as much as I understand it, chords are derived from scales, and scales are not derived from chords.

The Lydian mode in the natural key signature (no sharps, no flats) is..

F G A B C D E F (i.e. the "C scale" except it starts and ends on F)

The note relationship to the bass tonic (F) of each note is...

F → G = major 2nd
F → A = major 3rd
F → B = augmented 4th.
F → C = perfect 5th
F → D = major 6th
F → E = major 7th
F → F = perfect octave

The flattened 5th note of this scale is Cb. The interval F → Cb is a diminished 5th. As the original post indicates, the 4th note of the Lydian scale has the same pitch as the flattened 5th note of the scale. This means the scale for F Lydian with a flattened 5th would contain the notes...

F G A B B (i.e Cb) D E F – the repeated pitch of B/Cb doesn't make much sense to me from a scale perspective.

Just my 2¢ worth.

MY SONGS...
Audiophile BIAB 2025