Expert witness Todd Decker alleges “five or six points of similarity" between Perry's 2013 hit and the 2008 Christian rap song "Joyful Noise."

Day two of the copyright infringement trial over Katy Perry’s 2013 single “Dark Horse” was characterized by more than one instance of live singing, but it wasn’t the pop star who was giving the performance.

Instead, Todd Decker -- a musicologist and professor who serves as the chair of music at Washington University in St. Louis -- belted out some tunes during his testimony on Friday (July 19). Serving as the plaintiffs' expert witness, Decker is just one cog in an effort to prove that Perry and her “Dark Horse” collaborators, including songwriter-producers Lukasz "Dr. Luke" Gottwald and Max Martin, copied the underlying beat from Marcus Gray’s 2008 Christian rap song “Joyful Noise” without the permission of he or his co-plaintiffs, Emanuel Lambert, aka Da Truth, and Chike Ojukwu. (The lawsuit was first filed in 2014.)

Rather than sing the actual lyrics to either track, Decker instead sang numbers representing the pitch in each note of the two instrumental beats at issue -- both of which had been previously characterized by the musicologist as an eight-note “ostinato," a.k.a. a repeating sequence of musical figures within a song.

In Decker’s estimation, those ostinatos share “five or six points of similarity,” including pitch, rhythm, texture, pattern of repetition, melodic shape and timbre, or “the quality and color of a sound.” Additionally, he said, the “descending melodies” of both ostinatos are unique. “I have not seen another piece that descends in the way these two do,” he noted.

In studying the similarities between “Dark Horse” and “Joyful Noise,” Decker told the jury he had listened, hummed, sang along to and played both songs at a piano -- exercises that ultimately led him to determine that Perry and the other defendants (none of whom were present in the courtroom on Friday) had “borrowed” (aka "copied") the underlying beat from the latter track.

During cross-examination, defense attorney Christine Lepera attempted to poke holes in Decker’s claim regarding the ostinatos' alleged uniqueness. To this end, Lepera introduced a chart formulated by the defense’s own expert witness -- NYU music professor and musicologist Lawrence Ferrara -- illustrating that two much-older songs, “Jolly Old St. Nicholas” and “Merrily We Roll Along,” feature nearly-identical instrumental sequences.

To demonstrate this aurally, Lepera had Decker sing the ostinatos of all four songs in sequence. While he obliged, the musicologist countered that Ferrara’s chart had greatly oversimplified the complexity of the compositions, not to mention the sound recordings. “The most important tool is always listening” in attempting to establish borrowing, said Decker, noting that it was “the combination" of the elements in each ostinato, as opposed to the notes on the page, that had led to his determination.

In a continuation of the plaintiffs' arguments from the first day of trial, Gray took the stand again on Friday, with much of his testimony devoted to establishing that Perry and her “Dark Horse” collaborators would have had access to “Joyful Noise” prior to crafting their track. To this end, screen shots from both YouTube and MySpace were introduced showing that “Joyful Noise” had racked up combined streams of nearly five million prior to the release of “Dark Horse” in 2013. A screen shot showing that the track was available to buy as a digital download on Amazon was additionally introduced, though in their cross-examination the defense claimed there was no proof that the song had appeared on the site until after the lawsuit was filed.

The defense team further attempted to counter the perception of “Joyful Noise” as widely accessible to a mainstream audience during the years in question by noting the plaintiffs’ failure to provide any sales records for the song, set lists for concerts where it was allegedly performed or footage of those alleged performances. They additionally pointed out that by Gray’s own admission, roughly 70% of the venues where Gray claimed to have performed “Joyful Noise” were religious in nature, while a substantial portion of the other 30% were holding religious events at the time.

Also on Friday, defense attorneys continued to sow doubts as to the nature of Gray’s original agreement with Ojukwu, the creator of the underlying beat featured in “Joyful Noise.” Because the beat at issue was created by Ojukwu separately, the defense argues, “Joyful Noise” is itself a derivative work and therefore plaintiffs have no legitimate copyright claim in the case.

The involvement of Ojukwu (who testified yesterday) in the creation of “Joyful Noise” has been a persistent issue during trial. On Friday, the defense continued their attempts to silo Ojukwu’s beat from the overall composition, noting that rather than being listed as a co-writer in the liner notes to Our World Redeemed -- the album on which “Joyful Noise” appeared -- he is credited merely as a producer and did not originally sign a formal agreement for his beat to be used. Gray countered that argument by alleging a “synonymous” relationship between the terms “writer” and “producer” in the hip-hop genre, further noting that the album's liner notes do list Ojukwu’s company Renew Mind, implying his publishing rights in the composition and therefore linking the beat and the song itself as a unified entity.

Further clarified on Friday was the prior departure of “Joyful Noise” co-writer Lecrae Moore from the lawsuit, in which he was originally named as a plaintiff. In a seeming attempt to sully the lawsuit as a whole, the defense introduced a declaration filed by Moore roughly three weeks after the suit was filed in July 2014, in which the songwriter and performer claimed the suit was filed without his knowledge and requested for his name to be removed. In the declaration, Moore additionally signed over his rights in the “Joyful Noise” composition to Gray, Ojukwu and Lambert free of charge.

The trial is slated to pick up again on Tuesday with testimony from "Dark Horse" co-writer Max Martin.