What was the main recording studio for Metallica's 1991 album, The Black Album?

The main recording studio for Metallica’s 1991 album, The Black Album, was One on One Recording Studios.

The studio was located in Los Angeles, where Metallica began the album’s principal sessions in October 1990. The band continued working there through June 1991, making the project an unusually extended production for a major rock release.

Additional work took place elsewhere. Metallica spent about a week at Little Mountain Sound Studios in Vancouver, British Columbia, and later completed overdubs and mixing at A&M Studios in Hollywood.

One on One is therefore the album’s listed studio, even though it was not the only facility used. The same Los Angeles studio had also been used for ...And Justice for All, making it part of Metallica’s transition from its late-1980s sound to the more streamlined approach heard on The Black Album.