 Digital accordions have buttons for changing the registers of the bass buttons/chords and the right-hand manual, and an air valve for letting the air out of the bellows without making sound.Unlike a traditional acoustic accordion, though, the register buttons are not opening valves or other mechanisms to pass air over reeds and produce acoustic sound.Digital accordions have a sensor that detects bellows pressure, which affects the loudness, sustain, and in some instruments, the timbre of the synthesized or sampled sound.