Has anybody noticed....

[Bakuhatsu]

there was some hair band back in the 80's that pionered something they called the "golden throat" it was a small very sensitive microphone taped to the singers throat, and then plugged into his guitar. The mic would pic up whatever he was saying, but it would get distorted by his guitar, so it came out all multi-toned and metalic sounding.

In ayu's case however, I doubt the microphone has anything to do with it, all it takes is some simple soundboard mixing to change a song all you like. No preformer ever does a concert without someone mixing the tracks live at a soundboard, even if its just for level checking.