I don't think you have quite got the use of the word correct. Crack is not a reflexive verb.
You could say 'Mariah Carey's voice cracked', but not that that she cracked it herself.
It means that when she was singing, the sound suddenly changed, and sounded bad. It is similar to how boys' voices break when they are adolescent. Sometimes they break gradually, but sometimes they crack suddenly like that, often during speech.