String Ensemble,String Trio Viola,Violin - Digital Download SKU: A0.851865 By Katy Perry. By Bonnie McKee, Dr. Luke, Henry Walter, Katy Perry, Lukasz Gottwald, and Max Martin. Arranged by Caroline McCaskey. Pop. Score and parts. 12 pages. AltStrings #2071139. Published by AltStrings (A0.851865). This engaging, gig-ready arrangement of Roar is easy to read and fun to play! For String Trio (Two Violins and Viola).