In the late 1920s, British Radio became briefly and creatively entwined with a broader modernist culture. Largely through a series of spectacular programmes such as The Kaleidoscope (1928), made by the producer Lance Sieveking, the BBC started to develop an ‘art’ of sound. This episode has generally been passed over in histories of modernism and broadcasting: at best, it has been seen as a brief and whimsical piece of formal experimentation. But through examining Sieveking’s private papers, this article shows that this new art of sound was rich in meanings and symbolism, and had a wider influence than has hitherto been assumed. Sieveking drew heavily on his own life, which encompassed imprisonment and flying during the First World War, and a glittering array of social acquaintances, which connected him with the most advanced artistic thinking. This led him to find ways of representing in sound the subjective mental experiences and jumble of memories that so fascinated modernist artists in an age influenced by popular Freudianism. Sieveking’s life and writing also shows how he drew boldly from the visual language of experimental silent cinema at a critical moment in its own development. In creating a complex montage style for radio, Sieveking also anticipated some of the aesthetic devices that would be deployed in the coming era of sound on film. Sieveking and his programmes therefore illustrate a particular moment of British cultural history when the creative boundaries between different media were especially porous, with highly creative results.