 Recording was delayed due to surgery.When he left the hospital, he arrived back in the studio to find the rest of the band experimenting more than ever with electronic drum machines, something driven largely by guitarist The Edge's interest in dance and hip-hop music, and, given his weakness after the operation, he relented, allowing The Edge to continue using drum machines, which contributed heavily to the album's electronic feel.Mullen has had tendinitis problems throughout his career.