Bob Rock worked with Metallica at One on One Recording Studios during the Black Album sessions.
The Los Angeles facility was the principal studio for recording Metallica, with sessions running from October 1990 to June 1991. The band also spent about a week at Little Mountain Sound Studios in Vancouver, while later overdubs and mixing took place at A&M Studios in Hollywood.
Rock had not previously produced a Metallica album, and his methods challenged the band's established habits. He asked the members to perform more as a unit, encouraged a stronger live feel, and pushed James Hetfield to refine the lyrics. The prolonged sessions included many takes and intense disagreements.
The result marked a shift from the tightly constructed thrash style of the band's first four albums toward a slower, heavier, and more polished sound. The album's production is central to its broad appeal: the drums are powerful, the guitars are sharply defined, and Hetfield's vocals are more prominent in the mix.