In this paper the audio mastering process and the role of the audio engineer are studied from two viewpoints. Firstly, the mastering engineer’s stance towards music technology is described with the concepts of aesthetic and technical use of technological artefacts as well as the intrinsic and extrinsic properties of sound recording. Secondly, the relationship between the musical work and its medium is described with several examples encountered in the mastering process of the album Rules (2012), which consists of ten works from the 1960s and 1970s by the Finnish electroacoustic music composer and instrument designer Erkki Kurenniemi.