 Alexei Monroe called Kraftwerk the "first successful artists to incorporate representations of industrial sounds into non-academic electronic music".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.