Alright, so I've been working with arranging the song Blast! by Marcus Miller for my school band, and we were thinking about key signatures. Personally, I thought the song fell into the D Phrygian, or something similar, being that it starts on D but it has the D#/Eb in there as well. That might be incorrect, as it also has both the F and the F# at different parts. These could be accidentals, too... What I'm asking is, if it's in D Phrygian, wouldn't that relate to Bb Major/Ionian, therefore having 2 flats? Or would it go under D Minor/Aeolian, in which case it would relate to F Major/Ionian, and have 1 flat. Either way, accidentals could just be put to take care of any notes not included, but I'm just wondering for my own curiosity.