AceShowbiz - Metallica are crediting Bob Rock with getting frontman James Hetfield to "open up," leading to a "deeper and intense" direction for the band.
The iconic Canadian producer, engineer and musician was brought in to oversee the thrash metal icons' 1991 self-titled album, more commonly known as "The Black Album", which has been reissued, alongside a star-studded 53-track covers tribute collection, to mark the 30th anniversary of the seminal record.
And drummer Lars Ulrich admits the rockers were "hesitant" about working with Bob because they were all about being anti-establishment.
In an interview with The Sun newspaper, the sticksman explains, "Everything that had fuelled Metallica gave the middle finger to producers, record companies, the business, so we were hesitant about working with him. As we started understanding that Bob was trying to help us fulfil our ambitions, it settled down."
"He brought in words like 'soulful' and got James to open up as a singer. But I still didn't know if we'd see him again when we walked out of the studio after a year spent making the album."
"Only when we had the experience behind us did we become best friends and carried on working together for 15 years."
The studio wizard - who has also produced records for the likes of Motley Crue, Bon Jovi, Aerosmith, and David Lee Roth - shares the same sentiment as Lars, having previously recalled how much "deeper and intense" James' lyrics became.
He reflects, "It was quite a change. These guys, they were deeper. More intense. There were times when I was thinking about James' lyrics. I was thinking, 'This guy's as good as anybody.' He's intense. He's deep. I didn't grow up on Metallica. I just came in to help them with a record."
"With Metallica, they were just guys to me. I didn't cater to what they were. I catered to what they wanted to do. That's ultimately what a producer is."
The covers compilation, "The Metallica Blacklist", includes covers by an eclectic mix of artists, including Miley Cyrus, Sam Fender, St. Vincent, Phoebe Bridgers, Dave Gahan, Chris Stapleton, Corey Taylor, and Chase & Status.