He’s created sounds that have helped define Hip Hop culture, so it is safe to say Rick Rubin has worked with and is a part of music’s elite. The megaproducer’s talents have been admired far and wide—if not for his own skills, then for being able to bring out the sonic best of hitmakers. This includes his longstanding, applauded work with Jay-Z and Eminem.

In a recent interview on the Joe Rogan Podcast, Rubin gave some insight into the writing processes for the two Rap icons.

“I’ve worked with artists who do it completely different. Eminem will—he’s always writing in a book. Always writing, all the time. And he’s always got notebooks, writing.” Rubin asked Eminem if he was coming up with rhyme schemes or other tools to use in the future. The Detroit standout told him that he’ll never use 99 percent of what he writes down, but it was a practice to keep his mind “engaged in the process of writing and finding new ways to write.”

This way, when he “needs” something to come to him, it does so with ease because he keeps his mind active. Rubin also mentioned Jay-Z’s method in the studio. “[He] doesn’t write anything down.”

“He just listens to the beat and hums and then goes on the mic and 20 minutes later, just says a whole complicated verse—complicated verse,” said Rubin. “I don’t know how he can remember it, much less have just written it and just be able to do it, like, free. It’s crazy.”

Rubin also included a story about working on “99 Problems” with Jay, saying that Hov heard the beat, hummed along for 15 to 20 minutes, and then was ready to record. “No paper, no writing, nothing, and delivers the whole thing,” said Rubin. “[He] says ‘let’s try it again’ and does it again, and the words will be the same, but the phrasing will be different.”

“It’s more like an improvisational solo.” Watch Rubin detail how Jay-Z and Eminem approach their writing styles below.