Music producer Dr. Luke testified Tuesday in Katy Perry’s copyright infringement case for her 2013 hit “Dark Horse.”

Christian rapper Marcus Gray (aka Flame) accused Perry and her team of copyright infringement for his song “Joyful Noise,” alleging that the two songs are significantly similar.

Dr. Luke produced the song from a beat written by Henry Walter, also known by the name Cirkut, who testified Tuesday. He said the bass notes are too basic to be safeguarded by a copyright and told the jury that his team had never heard the track “Joyful Noise.” Since the Christian genre is substantially different to mainstream pop, he alleges there would have been no way for the team to have heard the track.

Perry stood before the court on July 18, also testifying that she wasn’t familiar with “Joyful Noise.” Cirkut and Dr. Luke brought the beats and bass notes to Perry, and she considered the song a “Trojan Horse” symbolizing female empowerment. Her attorney, Christine Lapera, also determined that the bass notes were too fundamental to be protected under a copyright. The notes can be heard in songs such as “Merrily We Roll Along” and “Jolly Old Saint Nicholas.”

“This is a common musical building block used in many compositions”, said attorney Christine Lepera. “This is very basic, like kindergarten-basic. [Gray and his co-writers] cannot monopolize that.”

In response, “Joyful Noise” co-writer Emmanuel Lambert (aka Da Truth) argued on July 18 that the track was praised and popular in the Christian rock community and that it is readily available on streaming services, so Perry’s team would have had access to the song.

Marcus Gray initially sued Perry back in 2014, saying that the song was similar enough to their 2008 hit “Joyful Noise” to constitute copyright infringement. The court hearing will continue shortly.