This is a fairly trivial question, but I've been curious about it for a long time: When you guys write out a chart for a modal piece of music, what do you write in the key signature?
For example: In E Mixolydian ...does it make sense at all to use 3 sharps in the key signature (since E mixo would have the same amount of sharps as A Ionian)?
I know if I saw 3 sharps in a key signature and someone told me it was because the music was in E mixo I'd be caught off guard. But taking a glance at it from a writing perspective, my mind tells me it makes sense.
I'm transcribing an Allman Bros. song for one of my students this week. A lot of it is E Mixolydian. I think most musicians would write out the key signature to denote what the root of the tonality is (i.e. 4 sharps since the tonic is "E" and the tonality is major) and then use accidentals any time you encounter a D-natural in the music.