The Ninth Circuit’s approach to music copyright cases has failed to provide artists with a clear landscape of the boundaries of copyright protection for creative works. Perhaps most disconcerting is the doctrine’s lack of rigid guidance as to which elements of a composition are protected by copyright. Since the court’s controversial ruling in Williams v. Gaye, which showcased the court’s failure to differentiate between protectable and unprotectable musical elements, the literature has taken a greater interest in analyzing the effects of this muddied doctrine. In their 2019 article, Christopher Jon Sprigman and Samantha Fink Hedrick theorize how the doctrine of the Ninth Circuit creates a “filtration problem” that allows weak copyright claims to pass through the court’s analysis and expose juries to irrelevant, potentially confounding, elements of a song. However, no one has yet quantified the effects of the filtration problem.

To fill this gap in the literature, this study conducts original quasi-experimental research to observe the extent to which mock jurors’ assessments of substantial similarity in musical compositions varies based on the elements included in the audio representations of compositions they listen to. Participants were randomly assigned to assess either a high-similarity song-pair or a low-similarity songpair. Within each group, different audio representations of the songs were presented, representing varying levels of filtration. Participants who listened to the most-filtered representation, the piano reduction, when assessing the low-similarity song-pair, were less likely to find similarity between the songs that those who listened to the commercial recordings. Conversely, for the high-similarity song-pair, those who heard the piano reductions were more likely to think the songs were substantially similar compared to those in the recording group.

The results of this study suggest that the effectiveness of filtration depends on the relative similarities of the elements filtered and those that remain across audio representations. The piano reduction, as the most-filtered representation, appeared to be a valuable tool for highlighting protectable elements and removing irrelevant factors that could confound jurors’ assessments. Based on these findings, this Article recommends that the Ninth Circuit adopt piano reductions as the standard audio representation for compositions played in music copyright trials. By doing so, the court can mitigate the detrimental effects of the filtration problem, making it more difficult for plaintiffs with compositionally dissimilar songs to succeed on copyright claims while simultaneously strengthening the claims of musician-plaintiffs against genuine instances of copying.