Bob Rock is credited with shaping the sound of Metallica’s 1991 album at One on One Recording Studios.
The band entered the Los Angeles studio in October 1990, beginning an eight-month recording period that ended in 1991. Rock’s approach differed from the methods used on several earlier Metallica albums: he wanted the musicians to perform more like a unified band rather than recording isolated parts.
Rock also pressed the group to refine its arrangements and lyrics. The result was a record with a broad, powerful guitar sound and more concise songwriting, while still retaining Metallica’s heavy identity.
The sessions were famously tense. Rock later described the experience as difficult, and the band and producer frequently argued about performances and production choices. Despite those conflicts, the collaboration produced Metallica’s commercial breakthrough and led to further work with Rock on later albums.