t's been 30+ years since I last played the flute. I rented a Yamaha flute from the local music store so that I could relearn it. I also own a Maestro open-hole flute. I noticed that when I play from low staff E up to above staff C (two lines above the staff) on both flutes, there is no change in tone quality when I depress the D# key. Just to make sure I'm playing the notes correctly, I played them using the TonalEnergy tuner. I don't see any difference in tone quality if I don't depress the D# key. What effect does pressing the D# key have on tone quality? If none, why depress it?