Vesti La Giubba

Twice they've used the piece on the show (that I know of). The first time being when Lazlo accidentally set it up for Gretchen to be wiped out and they had an actual clown singing it, the second when Lumpus was being punished by death clowning and he's tied to train tracks.

I've found numerous versions of the song but I can't find the specific performer for the one used in the cartoon and I really want to find it, does anyone know whose voice it might be?

"If you should need me, tap this staff three times on a wall."
"Magic?"
"No, it's just loud."