Which studio did Metallica primarily use to record The Black Album?

Metallica primarily recorded The Black Album at One on One Recording Studios.

The studio was located in Los Angeles, California, and served as the main recording site for the sessions that ran from October 1990 into 1991. The band also spent about a week at Little Mountain Sound Studios in Vancouver, British Columbia, and completed additional overdubs and mixing at A&M Studios in Hollywood.

The main sessions were demanding because producer Bob Rock wanted Metallica to record in a more collaborative way. Rock encouraged the musicians to play together and pushed for a live feel, while the band pursued the precision expected from a major studio album. The production process involved many takes, editing, overdubbing, and repeated mixing.

Because several locations were involved, lists of recording sites can look inconsistent. One on One is the principal studio named for the album, while Little Mountain and A&M were supporting locations. The answer therefore identifies the main studio rather than every facility connected with the record.