In a new interview with Guitar.com, Tony Iommi‘s longtime producer revealed how the Black Sabbath legend has crafted his guitar tone – and as you might expect from a man who had to basically invent metal guitar, he tends to go to extremes with his gear.

Mike Exeter has been working with Iommi for over three decades and is also well-known for working with the likes of UB40, The Specials, Jeff Beck, Cradle Of Filth and Judas Priest.

Over time, Exeter has become very familiar with the way a musician expresses whether they like what they’re doing or not.

“Tony is very easy for me to read,” Exeter says. “I know him so well, I can spot the facial expressions or body language. Sometimes it’s what he plays, other times it’s how he plays. If he does a certain trill, I know that means he’s not getting enough sustain from the amp. What he’s looking for is, ultimately, an extension of himself.”

He goes on to recall that the pair have a habit of listening to live footage from Paris in 1974 and compare it to the sound of the first two Black Sabbath albums, or the post-Ozzy years with Ronnie James Dio.

“When I listen to the first two Sabbath albums, they’re incredibly fuzzy,” Exeter says. “It’s a classic Laney sound. But he wasn’t using that in 1980 for the Dio albums. He’d switched to hotter Marshalls around that period. So there is no singular definitive sound for Tony, but he definitely has his own feel. I can pick him out from a mile off just because of the little things he does.”

He even lends some advice to players who have been inspired by Iommi’s tone. “To sound like Tony, you generally need P-90s going into a thick, soupy sound,” Exeter says. “It’s broken up, almost like speaker distortion. You might not think he was dialing in much gain, but trust me, he was on 11 for everything, because in the old days they had single-channel amps."

Read more at Guitar.com.