"The German term Neue Horspiel refers to ear-plays that neither adapt live theater nor create the illusion of it but, instead, exploit the unique possibilities of radio (audio) to create something that can exist only in sound. The pioneering anthology of such texts is Klaus Schoning's Neues Horspiel (1969). This book includes Max Bense and Ludwig Harig's Der Monolog der Terry Jo, which presents only the thoughts within the mind of a hospitalized woman whose recovery of consciousness is portrayed in her progressing from nonsensical oral sounds to articulate speech, and Ernst Jandl and Friederike Mayrocker's Funf Mann Menschen, which compresses fourteen stages of a man's life into fourteen vignettes, each dominated by a characteristic spoken sound."
Read more here. (It's by/about Momus.)