Kluster was a short-lived project of three musicians/artists/performers: Dieter Moebius, Hans-Joachim Roedelius and Konrad Schnitzler. They recorded two albums with Conny Plank in 1970, unprecedented in their experimental radicalism. Chaotic, apocalyptic (noise) improvisations (a sound later termed industrial), enriched with recited lyrics in places. The trio split up not long afterwards. Exchanging the K for a C, Roedelius and Moebius continued as a duo under the name of Cluster, whilst Conrad Schnitzler went solo. "Klopfzeichen" was the most radical album of the early German pop music avant-garde by a country mile. Its sounds and noises had nothing in common with the sequencer-generated electronic music emerging from Berlin or Düsseldorf. Kluster music was Angstmusik, the music of fear.