Metallica producer Bob Rock said he “didn’t get” the band’s classic track “Enter Sandman” when he first heard it, and didn’t think it should be the lead single from the group’s 1991 Black Album.

The single sold over a million copies worldwide and introduced Metallica to mainstream radio airplay. However Rock, who was still struggling to establish a relationship with the band, wasn’t certain of its pedigree when they began working on it.

“I remember Lars [Ulrich] saying, ‘Well, “Sandman” is the single,” Rock told Gibson TV recently (via Guitar World). “And I’m going, ‘What?’ To me it was like, I didn’t get it yet. Because all the lyrics weren’t there. I was thinking ‘Holier Than Thou,’ only because that kind of energy was up-tempo and that kind of works for me.” He added: “What do I know? It ended up being ‘Sandman’ – obviously a good choice.”

He also recalled the challenge of opening communications with Metallica, especially when he wanted them to change from the standard E guitar tuning they’d always used to the frequently-used “drop-D” arrangement, which is regarded as heavier and offers easier access to metal power chords. “Maybe six songs in, I noticed that every song was in E,” Rock explained. “And I just went, ‘Why is everything in E?’ And James [Hetfield] looked at me like he wanted to kill me and he says, ‘It’s the lowest note.’ And I’m going, ‘Oh.’”

Rock told Hetfield that bands including Black Sabbath and Motley Crue used drop-D and told them to try it out. “The next song was ‘Sad But True’ and they just played it once and it was just like, ‘Holy fuck!’ They started to like me a little bit on that day. Just a little bit. I think they started having lunch with me.”

Bob Rock on Gibson TV