Christine's voice

[igenlode]

It's interesting that Raoul in the book is actually dismayed by Christine's uninspired singing -- thus proving that (a) he isn't just some fashionable fribble attending the opera as part of a society ritual but actually cares about music and takes an interest, and (b) he is attracted to her for herself and not for her talent, and thus Erik's contribution has absolutely nothing to do with it :-p

If Christine couldn't sing, Erik would have had no interest in her whatsoever, but she would still be Raoul's long-lost sweetheart.