with britney spears. ♪ hit me baby one more time the pair collaborated on "since u been gone" kelly clarkson's gone >> i have a lot of a & r people i'm friends with to this day who are like, yeah, you know, i passed on that song. i think one of the things that made the song special is her voice on that song. ♪ yeah yeah >> reporter: that song's radio friendly chorus would come to typify dr. luck's sound. with max martin as his mentor, luke quit "snl" to focus on producing. >> i'm looking for voices that are distinctive. that's the most important thing to me.e. ♪ ♪ you think i'm pretty ♪ without any makeup on >> reporter: one such voice, katy perry. her song "teenage dream" sounds like the simplest of pop songs. a hit brought into being here at hollywood's conway studios, thanks to an astonishing 182 different tracks. as dr. luke showed us. >> the first thing that it started with was the guitars. ♪ she does all her backgrounds. she does all them. so the lead is just -- ♪ you think i'm pretty without any makeup ♪ when you do a chorus, there's three right here, give it -- ♪ you make me feel like