180 gram reissue. Originally released in 1971 on German label Schwann/AMS Studio, one of two albums recorded in Dusseldorf in 1970. These two albums featured members Dieter Moebius, Hans-Joachim Roedelius, and Konrad Schnitzler and were unprecedented in their experimental radicalism. Klopfzeichen was the most radical album of the early German music avante-garde by a country mile. Conny Plank was on board early as the sound engineer and added seamless character to this angst-ridden experimental music. Konrad Schnitzler left after these records and continued on as a solo artist. The band then continued on as Cluster. Liner notes by Asmus Tietchens.