I have to play some harp in my band and I just want to confirm my information on which key to use? A perfect fourth and a perfect fifth will work won't it? So if the song is in G, then I can play a C or D Diatonic Harmonica with the song. Correct? Any other pertinent info will be appreciated. The song I am playing is in G minor pentatonic I think. Is the formula the same? Can I use a C or D Diatonic harp?