Super producer Rick Rubin has seen it all.

The 59-year-old has hit records in every genre, going back decades.

Rubin has worked with both JAY-Z and Eminem and during a chat with Joe Rogan he broke down the difference between the two legends.

“You’ll see Eminem, he’s always writing in a book. Always writing all the time. And he’s always got notebooks and writing. And I ask him, like ‘are these all rhymes to use?’ and he’s like ‘nah, 99% of what I write I’ll never use. It’s just to stay engaged in the process of writing and finding new ways to write so that when I need it it just comes. An then Jay-Z doesn’t write anything down and he just listens to the beat and hums, hums, and then goes on the mic 20 minutes later and says a whole complicated verse. I don’t know how he can remember it much less have just written it and just be able to do it like freely, it’s crazy.”

Rubin then spoke about recording "99 Problems" with Hov.

“No no no, this is for a record. Like, when we were recording ’99 Problems’ I played the beat for him, he likes the beat, and then he says ‘okay, just keep playing it.’ He then sits in the back of the control room on the couch and you just hear him humming (hums along). As I say 15 or 20 minutes, and then he jumps up and is like ‘okay, I got it’.”

“And he goes in, no paper, no writing, nothing. And he delivers the whole thing and then says ‘let’s try it again’ and then he does it again. And th words will be the same but the phrasing will be different so it’s more like an improvisational solo. If you have a melody you can play the same melody with putting emphasis on different parts of it. So he does it, it’s not the same. The words are the same, or close to the same. But the feeling of it and the rhythm of it changes when he does it again and he does it a few times.”