Christopher Rouse’s Requiem has been described as a “musical terror.” An hour and a half in length and comprising 16 movements, the epic choral work is so demanding that it’s taken five years to finally get it to an audience. This week, Grant Gershon conducts the Los Angeles Master Chorale, Los Angeles Children’s Chorus and renowned baritone Sanford Sylvan in the world premiere of Rouse’s “emotionally raw musical journey,” which began as a work commissioned to celebrate the 2003 bicentennial anniversary of Hector Berlioz’s birth, but which took an unexpected turn in 2001, with the shattering events of 9/11. The Requiem became both an homage to Berlioz, whose own Requiem profoundly influenced Rouse, and a memorial to, in the composer’s words, “all who have died as well as those who have survived and grieved for them.” The piece is Pulitzer Prize–winning Rouse’s largest and most ambitious work to date, but the Master Chorale is up to the challenge. As the composer happily observes, “I know that the piece will hold no musical terrors for them!” Walt Disney Concert Hall, 111 S. Grand Ave., dwntwn.; Sun., March 25, 7 p.m.; $19-$109, $10 student rush. (800) 787-5262 or www.lamc.org.