This chapter discusses the early history of electronic signal processing through Mexican composer Carlos Chávez’s 1937 book on electronic sound, Toward a New Music.  Chávez’s text, which offers a thrilling exploration into early 20th-century electronic sound practices, demonstrates an account of music, radio, and cinema defined by a common scientific infrastructure and continued pattern of technological codependence between media. Emphasizing Chávez’s discussion of cinema and sound mixing as indicative of the relationship between media forms, I propose that Chávez’s work reshapes our understanding of sound technology from an account that privileges medium specificity toward an understanding that explores the shared technical infrastructure of sound recording and mass culture.  Alongside discussing Chávez’s often prescient book, I examine how recording engineers and technicians working in Hollywood, telecommunications, and technology companies such as RCA also considered sound mixing early history.