This essay examines the sonic archive of tape recording artist Tony Schwartz, in particular his 1955 Folkways album Nueva York: A Tape Documentary of Puerto Rican New Yorkers. Working from assumptions located in sound studies, I argue that Schwartz's recordings are essential listening for two reasons. One, Schwartz's meticulous attention to what he called the “sounds of [his] times”—and, I would add, of his place—helps scholars reconstruct the 1950s from a new vantage point: the ear. Two, Schwartz understood something that sound studies scholars are only beginning to tease out. Sound is not merely a scientific phenomenon—vibrations passing through matter at particular frequencies—it is also a set of social relations. “Splicing the Sonic Color-Line” begins by theorizing the mutually constitutive relationship I find between sound, listening, and race as the “sonic color-line.” Next, original archival material is used to reconstruct the historical soundscape of Tony Schwartz's street recordings and reveal the sonic color-line as the aggregated racialized constraints and protocols regarding sound that Nueva York is both embedded in and struggles against. Finally, I trace the way in which Schwartz's “sono-montage” in Nueva York splices the sonic color-line, translating mainstream representations of the so-called homogenous noise of Puerto Rican life into textured, meaningful sound to assimilated (white) Americans. Nueva York is symptomatic of the ways in which listening experiences reflect and generate ideas about racial difference and its historical connection to American citizenship.