i try to explain negative harmony with a photo.
You have to take the c major scale and subdivide it in stables notes(they don't need to resolve) and active note (need to resolve in stables notes)
Then subdive the octave between E and Eb and you find the point 2
apply this "opposite" note on C major scale and you will find the C minor! The stable note in C major, will stay stables in C minor. Same to actives notes
Apply that to th harmonization of C major scale and you will find the negative harmonization of C major!
Then you can substitute chords from C major to their negative form
I hope this can help you,
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