In October 1990, Metallica entered One on One Recording's studio in North Hollywood to record its next album. Bob Rock, who had worked with Aerosmith, The Cult, Bon Jovi, and Mötley Crüe, was hired as the producer. "Metallica"also known as "The Black Album"was remixed three times, cost , and ended three marriages. Although the release was delayed until 1991, "Metallica" debuted at number one in ten countries, selling 650,000 units in the U.S. during its first week. The album brought Metallica mainstream attention; it has been certified 16 times platinum in the U.S., which makes it the 25th-best-selling album in the country. The making of "Metallica" and the following tour was documented in "A Year and a Half in the Life of Metallica". The tour in support of the album, called the Wherever We May Roam Tour, lasted 14 months and included dates in the U.S., Japan, and the UK. In September 1991, 1.6 million rock music fans converged in Moscow to enjoy the first open-air rock concert to be held in the former Soviet Union, part of the Monsters of Rock series. In April 1992, Metallica appeared at The Freddie Mercury Tribute Concert and performed a three-song set. Hetfield later performed "Stone Cold Crazy" with the remaining members of Queen and Tony Iommi.