A Variophon is an electronic wind instrument invented in 1975 by researchers at the University of Cologne. It synthesizes sounds using the principle of most common brass instruments, creating sounds based on the vibration of the player's lips and breath and the resonance in a particular body. For this purpose, the instrument is played using a pipe-controller, while the pitch is controlled either by keys on the pipe itself or in later models, an external keyboard. The Variophon can alternate in timbres, imitating a variety of wind instruments, ranging from the harmonica to clarinet, saxophone or tuba. The variophon has a processing unit, dubbed "the music cockpit" which the controller must be connected to. The controlling voltages of the blow controller and keys combine to influence the shape, width, and height of the electric pulses. The pulses it creates are modeled by the pulse formations of real wind instrument sounds, which is how the variophon replicates the sounds of these instruments.