It’s time to put some of that theory knowledge to good use. You have your time signature, you have some melody, it’s time to figure out the key signature of this song. You need a healthy knowledge of scales for this. Being familiar with the Circle of 5ths would also be incredibly helpful. You will need several measures of dictation already done to determine a key signature.
- Take a note, which accidentals (sharps or flats) keep popping up in your melody? An accidental that only occurs once can probably be ignored, but if you see Ab over and over, it’s probably in your key signature. Casino Night Zone includes Eb, Gb, Ab, and Bb. The Gb and Eb happen pretty rarely, so we can probably ignore them.
- Now compare this to the Order of sharps (F# C# G# D# E# A# B#) or Order of flats (Bb Eb Ab Db Gb Cb Fb). You will never have both sharps AND flats in the same key signature, so you may have to use enharmonic spellings to make sure all your accidentals are either one or the other. (Rather than Ab and D#, use Ab and Eb, or G# and D#.)
- When a song has flats, I move back one flat in the order of flats to determine my key signature. One flat before Ab is Eb, so the song would be in the key signature of Eb. Sharps work a little differently. For sharps, the key signature is a half-step above the last sharp in your order of sharps. ( eg.: A half step above C# is D.)
- Add the key signature to the beginning of your notation. Now you don’t have to add in every single accidental, because most of them should be automatically indicated by the key signature.
- If you are having trouble pinpointing the key signature, feel free to leave the arrangement in C major (no sharps or flats). You will just have to mark every single accidental until you identify the key signature. This is the option I’m using for Casino Night Zone, because the accidentals are not consistent enough to indicate a signature. (It sounds like it’s using a blues scale, but I’m not taking the time to figure that out today. I should’ve picked a better example. :-/)