Charlie Chan à l'opéra

According to my sources, there seems to be a slight disagreement on the singing in this movie. Denis Gifford's Karloff bio says that Karloff did his own singing (and he could have; he was a fair baritone and sang in the Dulwich College chorus). Oscar Levant's autobiography claims that Karloff was dubbed. Oscar Levant, however, seems to have been writing from an unreliable memory, as he gets other details wrong including the movie synopsis. There are three singing voices heard in the movie: soprano, tenor, and baritone. The tenor was never seen, but was heard onstage while Chan and Number One Son were backstage. Both actresses playing sopranos were synching to the same recording. Karloff may also have been synching to a recording, but it could well have been his own, both for the reason given above and because Levant's opera was written for the movie--no previous recordings existed at the time, and why would the studio have spent extra money on a second singer for a B-budget film when they already had someone on the film who could handle the baritone singing? (Even the Faust costume worn by both baritones onstage was secondhand--it was first worn by Lawrence Tibbett in "Metropolitan", filmed earlier in 1936!)