Totally non-commercial, experimental, with tape manipulation and extensive use of echo, these groundbreaking album comes from the first line-up of the renowned avant-garde/electronic group Cluster. On 23 November 1970, Joseph Beuys pupils and art students Conrad Schnitzler and Dieter Moebius as well as the self-taught artist Hans-Joachim Roedelius entered as the ensemble Kluster the Rhenus Studio in Cologne, which was still owned by a church-run publishing house at the time. Supported by the legendary producer Conny Plank, the trio recorded their first and by far the most radical album of the early German pop avant-garde, a movement later named „industrial“.

The liner notes explain the musicians’ working method: „Kluster play on standard instruments (piano, electric guitar, cellos, percussion and electric organ), but these sounds are recorded via contact microphones, transformed, manipulated, distorted, chopped up and played back through loudspeakers.“ Released by the German label Schwann AMS Studio in a limited edition of just 300 copies, the artwork Klopfzeichen captivates with its unique plastic relief cover, supplemented by a text and image insert. Following their second album a year later, the group split up, the rest is music history. As one of the rarest German experimental LPs ever, it is virtually impossible to find today.