Nevermind producer Butch Vig recently served as the keynote speaker for Yellow Phone Music Conference, where he claimed Kurt Cobain and Nirvana rehearsed 10 hours a day for a period of six months before recording their 1991 mega-hit.

That comes out to roughly 1,800 hours of work, which is probably a hell of an exaggeration.

Still, the there's no doubting the grunge gods put in a ridiculous amount of time before hitting the studio.

"Some people don't know this, but before they came in, they rehearsed every day for six months, like 10 hours a day," Vig said (Rolling Stone). "Kurt, contrary to the slacker attitude, wanted to have a hit record. He wanted to make a really good-sounding album."

Vig also stated that there was an ulterior motive for working so hard.

"Part of the reason they rehearsed for 10 hours a day was they were living in a really floppy, sh--ty apartment up in the northwest, and the rehearsal space had a space heater," he said. "So they would go in there and it would be warm and they would go in there and play until 10, 11 o'clock at night and then they'd go back to their apartment. But they were tight."

The 59-year-old producer also reminisced about forcing Cobain to redo the famous "Smells Like Teen Spirit" intro in order to fit Dave Grohl's drum opening.

"I remember torturing Kurt for about half an hour, trying to play it to get the timing so when Dave came in with the drum fill [it would be right]," Vig said. "He was not happy about that, but he eventually got it. But it's the same chord progression all the way through, and you can feel the way the band plays, especially the way Kurt sings, they are going for it. And again it's that human performance thing. I think that's one of the reasons the record still sounds good. It doesn't sound dated to me. It just sounds like an amazing performance and it's a killer song."

In its fourth year, the Yellow Phone Music Conference took place in early September.

"Yellow Phone's commitment to bridging the gap between the musician and the industry is something that really resonates with me," Vig said. "The fact that such a progressive conference is taking place in the area I grew up in is fantastic — the industry could use more of that."