Previous studies have shown that pairing a film excerpt with different musical soundtracks can change the audience’s interpretation of the scene. This study examined the effects of mixing the same piece of music at different levels of loudness in a film soundtrack to suggest diegetic music (“source music,” presented as if arising from within the fictional world of the film characters) or to suggest nondiegetic music (a “dramatic score” accompanying the scene but not originating from within the fictional world). Adjusting the level of loudness significantly altered viewers’ perceptions of many elements that are fundamental to the storyline, including inferences about the relationship, intentions, and emotions of the film characters, their romantic interest toward each other, and the overall perceived tension of the scene. Surprisingly, varying the loudness (and resulting timbre) of the same piece of music produced greater differences in viewers’ interpretations of the film scene and characters than switching to a different music track. This finding is of theoretical and practical interest as changes in loudness and timbre are among the primary post-production modifications sound editors make to differentiate “source music” from “dramatic score” in motion pictures, and the effects on viewers have rarely been empirically investigated.