Johnny Depp will have to take a singing test to win his latest part.

The actor is vying for the lead role in a big screen version of Stephen Sondheim's Sweeney Todd, but the composer fears his voice may be to rock 'n' roll for the part.

A spokesman said: "He wants to make sure that all versions of his works are the best possible."

Tim Burton, with whom Depp has worked may times, will direct the movie, due out in 2008.