Which studio did Metallica use as the main recording location for The Black Album?

Metallica used One on One Recording Studios in Los Angeles as the main recording location for The Black Album.

The album's sessions ran from October 1990 to June 1991, making the project a lengthy and demanding production. The band also spent about a week at Little Mountain Sound Studios in Vancouver, British Columbia, while additional overdubs and mixing took place at A&M Studios in Hollywood.

One on One was therefore the principal studio, not the only facility connected with the record. The Los Angeles setting became closely associated with the album's creation and with the period documented in the film A Year and a Half in the Life of Metallica.

The record's polished sound reflected both the studio work and Bob Rock's production methods. He encouraged the musicians to record as a unit, use harmonic vocals, and perform many takes. Those changes helped distinguish the album from Metallica's earlier recordings.