This article responds to Alan Lomax's pronouncement that the mid-twentieth century constituted ‘the age of the golden ear’, when ‘a passionate aural curiosity overshadowed the ability to create music’. It examines a project born out of Lomax's own aural curiosity and his foregrounding of recording technology – the Columbia World Library of Folk and Primitive Music (1955) – using it to sound out the history of mid-century ethnographic field recording. By retracing the production of the World Library, this article explores the various agencies compressed into the audible exteriors of field recordings, as they were produced by and for specific technologies and formats, circulated through international networks, and as they became part of the aural public sphere of post-war Europe. It concludes by considering some of the implications of this sonic labour as field recordings find their way into new, digital, listening environments.