A concept album exploring themes of broadcast communications, Radio-Activity marked Kraftwerk's return to more obtuse territory, extensively utilizing static, oscillators, and even Cage -like moments of silence to approximate the sense of radio transmission; a pivotal record in the group's continuing development, the title track -- the first they ever recorded in English -- is their most fully realized electro-pop effort to date, while "The Voice of Energy" precipitates the robot voice so crucial to their subsequent work.