Producer Bob Rock recently spoke to MusicRadar.com about his work on METALLICA's mega-selling self-titled LP, popularly known as the "Black Album," which is celebrating its 20th anniversary next month."It wasn't a fun, easy record to make," said Rock. "Sure, we had some laughs, but things were difficult. I told the guys when we were done that I'd never work with them again. They felt the same way about me." On METALLICA's more "mainstream" songwriting approach: "They had broken through to one level, but they still weren't on mainstream radio. When they came to me, they were ready to make that leap to the big, big leagues. A lot of people think that I changed the band. I didn't. In their heads, they were already changed when I met them." On how drummer Lars Ulrich changed his playing style in order to suit the more straight-forward nature of the new material: "I noticed that Lars played to James' [Hetfield] guitar, much like the way that Keith Moon played to Pete Townshend. That's fine for some bands, but not every one. Lars wanted METALLICA to groove more. AC/DC's 'Back In Black' was a big reference point as a rock record that grooved. I told him that in order to get that feel, he had to be the focal point musically. So on certain songs, the band played to Lars. They followed him. It made a real difference." On James Hetfield's lyrical approach: "He wanted to go deeper with his writing. He wanted his songs to really matter. We talked about the great songwriters, like Dylan and Lennon and Bob Marley, and I think he saw that he could write for himself but still touch other people. It was a struggle for him, but he had a tremendous breakthrough as a writer." On "Enter Sandman": "I insisted on the band playing live in the studio. They had never done that before all of their previous records were recorded in sections. I told them, 'You're a great live band. That vibe is crucial to the album.' "On 'Sandman', I asked Jason [Newsted] to play more like a bass player and less like a guitarist. Put that with the new perspective Lars had on drums and we had a song with a killer groove. "At first, based on the music and the riff, the band and their management thought it could be the first single. Then they heard James' lyrics and realized the song was about crib death. That didn't go over well. "I sat down with James and talked to him about his words. I told him, 'What you have is great, but it can be better. Does it have to be so literal?' Not that I was thinking about the single; I just wanted him to make the song great. It was a process, him learning to say what he wanted but in a more poetic and open sort of way. He rewrote some lyrics and it was all there the first single." On "Sad But True": "They played me the demo, and I told them I thought it was the 'Kashmir' of the '90s. The riff was astounding. To my knowledge, they never had anything so heavy, so punchy and powerful. Rhythmically, I could tell it had the potential to be absolutely crushing! "We were in pre-production, which was uncomfortable because nobody had ever made them go through their songs in such a deliberate way before, and six songs in, 'Sad But True' came along. Suddenly, I realized that every song, including this one, was in the key of E. "I brought this to the band's attention, and they said, 'Well, isn't E the lowest note?' So I told them that on MTLEY CRE's 'Dr Feelgood', which I produced and METALLICA loved, the band had tuned down to D. METALLICA then tuned down to D, and that's when the riff really became huge. It was this force that you just couldn't stop, no matter what. Read the entire article from MusicRadar.com.