Final overdubs and mixing for Metallica's 1991 album took place at A&M Studios in Hollywood.
Most of the album's recording work began at One on One Recording Studios in Los Angeles in October 1990. Metallica also spent about a week at Little Mountain Sound Studios in Vancouver, British Columbia. The final overdubs and mixing were completed at A&M Studios in Hollywood during June and July 1991.
This multi-studio process occurred during a demanding eight-month recording period. Producer Bob Rock encouraged the band to work more collaboratively and to capture a stronger live feel. The musicians recorded many takes, then selected and edited the best performances into finished tracks.
A&M Studios is therefore associated with the album's final production stage rather than the principal beginning of the sessions. Confusing it with One on One is easy because One on One is the studio most closely identified with the initial recording phase.