Deep Purple are an English rock band formed in Hertford in 1968. They are considered to be among the pioneers of heavy metal and modern hard rock, although their musical approach changed over the years. Originally formed as a progressive rock band, the band shifted to a heavier sound in 1970. Deep Purple, together with Led Zeppelin and Black Sabbath, have been referred to as the "unholy trinity of British hard rock and heavy metal in the early to mid-Seventies". They were listed in the 1975 Guinness Book of World Records as "the globe's loudest band" for a 1972 concert at London's Rainbow Theatre, and have sold over 100 million albums worldwide. Deep Purple have had several line-up changes and an eight-year hiatus (1976–1984). The 1968–1976 line-ups are commonly labelled Mark I, II, III and IV. Their second and most commercially successful line-up featured Ian Gillan (vocals), Jon Lord (organ), Roger Glover (bass), Ian Paice (drums), and Ritchie Blackmore (guitar). This line-up was active from 1969 to 1973, and was revived from 1984 to 1989, and again from 1992 to 1993. The band achieved more modest success in the intervening periods between 1968 and 1969 with the line-up including Rod Evans (vocals) and Nick Simper (bass, backing vocals), between 1974 and 1976 (Tommy Bolin replacing Blackmore in 1975) with the line-up including David Coverdale (vocals) and Glenn Hughes (bass, vocals), and between 1989 and 1992 with the line-up including Joe Lynn Turner (vocals). The band's line-up (currently featuring Ian Gillan, and guitarist Steve Morse from 1994) has been much more stable in recent years, although organist Jon Lord's retirement from the band in 2002 (being succeeded by Don Airey) left Ian Paice as the only original Deep Purple member still in the band. Deep Purple were ranked number 22 on VH1's Greatest Artists of Hard Rock programme and a poll on British radio station Planet Rock ranked them 5th among the "most influential bands ever". At the 2011 Classic Rock Awards in London, they received the Innovator Award. In October 2012, Deep Purple were nominated for the first time for the Rock and Roll Hall of Fame, but were not voted in the following March. In October 2013, the band was announced as a Hall of Fame nominee for a second time, but again was not voted in.