Kraftwerk used a custom-built vocoder on their albums "Ralf und Florian" and "Autobahn"; the device was constructed by engineers P. Leunig and K. Obermayer of the Physikalisch-Technische Bundesanstalt Braunschweig. Hütter and Schneider hold a patent for an electronic drum kit with sensor pads, filed in July 1975 and issued in June 1977. It must be hit with metal sticks, which are connected to the device to complete a circuit that triggers analog synthetic percussion sounds. The band first performed in public with this device in 1973, on the television program "Aspekte" (on the all-German channel Zweites Deutsches Fernsehen), where it was played by Wolfgang Flür. They created drum machines for "Autobahn" and "Trans-Europe Express"