Green Day's sixth studio album, Warning, was recorded from March - April 2000 at Studio 880 in Oakland, California. This was the first album since Green Day signed to Reprise that Rob Cavallo did not fully produce (though he was still an executive producer for the album). This album marked a significant change in Green Day's sound with the band deciding to include a wider variety of instruments, most notably more acoustic guitars. The album received mixed criticism after its release, but still debuted at #4 on the Billboard chart. The album has sold over 3 million copies worldwide since its release.