Its natural minor with the exception of that note. If i change it to harmonic or melodic minor, it changes the other note relationships….
This is the song with the harmony….. At the 4:50, 5:20 and 9:15 marks, the fourth note I play is the note in question. (i play B, A, B, Bb)
I was using a Boss multi unit from the 90s for these harmonies, and it never glitched on the Bb… (that board was eventually stolen)
I could record sound examples if necessary.
