"Wish You Were Here" is the ninth studio album by the English progressive rock group Pink Floyd, released in September 1975. It explores themes of absence, the music business and former band member Syd Barrett's mental decline. Inspired by material the band composed while performing across Europe, Wish You Were Here was recorded in numerous sessions at London's Abbey Road Studios. The premise of the album was based on a song written by the band called "Shine On You Crazy Diamond". "Shine On" was a tribute to Barrett, who, coincidentally, made an impromptu visit to the studio while it was being recorded. It was lead writer Roger Waters's idea to split the "Shine On" in two parts and use it to bookend the album around three new compositions, forming a new concept similar to their previous album, The Dark Side of the Moon. As with that record, the band made use of studio effects and synthesizers for Wish You Were Here. Additionally, the band brought in guest singers to supply their vocals to some tracks, another feature from their previous album. These singers included Roy Harper, who provided the lead vocals on "Have a Cigar", and The Blackberries, who made guest background vocals on "Shine On". Wish You Were Here was released in September 1975. The album became an instant commercial success and record company EMI was unable to print enough copies to satisfy demand. Although it initially received mixed reviews, the album has since been acclaimed by critics and appears on Rolling Stone's list of "The 500 Greatest Albums of All Time". Band members Richard Wright and David Gilmour have each declared Wish You Were Here their favourite Pink Floyd album.