 Some instruments referred to as "MIDI accordions" may be hybrid acoustic-electronic instruments, in that they contain the traditional acoustic elements (reeds, bellows, valves) with sensors and electronic circuitry that converts button and key presses and bellows pushing and pulling into MIDI messages.These MIDI messages can be plugged into an external synthesizer, sampler, or sound module to produce sounds.A hybrid acousic-electronic accordion may have an "all off" register switch which stops all of the acoustic reed sounds; this enables a player to use an entirely synthesized sound (electronic synthesizer strings or trumpet, for example), or play with headphones plugged into a synth module for night-time practice.