Question: Which band along with two other British bands is referred to as the "unholy trinity of British hard rock and heavy metal in the early to mid-seventies" whose performance was featured in a 2011 studio compilation album at the BBC's Maida Vale Studios?

full_context: Document 1: Singles 1968–1971: Singles 1968–1971 is a box set compilation of singles by The Rolling Stones spanning the years 1968 to 1971. The latest in a series of repackages by ABKCO Records, who licence The Rolling Stones' 1963–1970 recorded works, "Singles 1968–1971" is the third of three successive volumes to commemorate their non-LP releases during this era.
Document 2: Scandinavian Nights: Scandinavian Nights is a double live album by the British hard rock band Deep Purple. It was originally recorded by Swedish National Radio for a radio show called "Tonkraft" at the Stockholm Konserthuset on 12 November 1970, but not released until 1988. The tapes were re-mixed by Tom Leader at Angel Studios in London. It remains the prime example of the early Mk II set list and ferocious concert dynamics. The set list comprises songs from the album "Deep Purple in Rock" and long instrumentals from earlier albums. The two songs "Mandrake Root" and "Wring that Neck" took up half the concert in the early days, until the "Fireball" tour.
Document 3: Deep Cuts, Volume 1 (1973–1976): Deep Cuts, Volume 1 (1973–1976) is a compilation of Queen tracks between 1973 and 1976. Unlike other compilations released by Queen, "Deep Cuts" contains songs which are largely not as well known as Queen's hits. The album was released on 14 March 2011 as part of Queen's 40th anniversary. "Deep Cuts Volume 1" was released at the same time Queen's first five albums ("Queen", "Queen II", "Sheer Heart Attack", "A Night at the Opera", and "A Day at the Races") were re-released. The songs picked were all personal favourite songs, that were not hits, selected by Brian May, Roger Taylor, and Taylor Hawkins (the drummer for the Foo Fighters). It is the only release to feature the complete ending of "The March of The Black Queen" (on "Queen II" it segues to "Funny How Love Is") and of "Ogre Battle" (on "Queen II" it segues to "The Fairy Feller's Master-Stroke"). The three songs "Tenement Funster", "Flick of the Wrist" and "Lily of the Valley" all segue into each other just as on the original "Sheer Heart Attack" album.
Document 4: The Who: The Who are an English rock band that formed in 1964. Their classic line-up consisted of lead singer Roger Daltrey, guitarist and singer Pete Townshend, bass guitarist John Entwistle, and drummer Keith Moon. They are considered one of the most influential rock bands of the 20th century, selling over 100 million records worldwide and holding a reputation for their live shows and studio work.
Document 5: BBC Sessions 1968–1970: BBC Sessions 1968–1970 is a 2011 studio compilation album featuring performances by the British hard rock band Deep Purple that were recorded at the BBC's Maida Vale Studios, London, and originally broadcast on various BBC Radio shows from 1968 through 1970. "BBC Sessions 1968–1970" is a two-disc set collecting all the surviving sessions in the BBC archives.
Document 6: Uriah Heep (band): Uriah Heep are an English rock band formed in London in 1969. Twelve of the band's albums have made it to the UK Albums Chart ("Return to Fantasy" reached No. 7 in 1975) while of the fifteen "Billboard" 200 Uriah Heep albums "Demons and Wizards" was the most successful (#23, 1972). In the late 1970s the band had massive success in Germany, where the "Lady in Black" single was a big hit. Along with Led Zeppelin, Black Sabbath and Deep Purple, Uriah Heep had become one of the top rock bands in the early 1970s.
Document 7: Blue Suede Shoes: A Rockabilly Session: Blue Suede Shoes: A Rockabilly Session was a televised concert that was taped live at Limehouse Studios in London, England on 21 October 1985. The show featured rock n' roll pioneer Carl Perkins along with friends as guest stars, including Eric Clapton, former Beatles George Harrison and Ringo Starr, as well as Dave Edmunds who acted as musical director for the show. Most of the repertoire performed in the concert consisted of Perkins' classic rockabilly songs from the 1950s. It was directed by Tom Gutteridge. The concert special was originally broadcast in 1985 on Channel 4 in the UK and on Cinemax in 1986 with introductory comments by Johnny Cash, Roy Orbison, and Jerry Lee Lewis. The show was shown on Channel 4 on January 1, 1986. Perkins performed 16 songs, with two encores, in an extraordinary performance. Perkins and his friends ended the session by singing his most famous song, 30 years after its writing, which brought Perkins to tears. The concert is a memorable highlight of Carl Perkins' later career and has been highly praised by fans for the spirited performances delivered by Perkins and his famous guests. It was the first public performance by George Harrison in more than ten years An edited version of the program is available for viewing on YouTube.
Document 8: List of heavy metal festivals: This is an incomplete list of heavy metal festivals. Heavy metal (or simply metal) is a genre of rock music that developed in the late 1960s and early 1970s, largely in the United States and the United Kingdom. With roots in blues rock and psychedelic rock, the first heavy metal bands such as Led Zeppelin, Black Sabbath and Deep Purple attracted large audiences, and during the late 1960s and mid-1970s these band and others in their genre were featured at a number of historic rock festivals. Judas Priest helped spur the genre's evolution by discarding much of its blues influence.
Document 9: Deep Purple: Deep Purple are an English rock band formed in Hertford in 1968. The band is 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.
Document 10: Led Zeppelin: Led Zeppelin were an English rock band formed in London in 1968. The group consisted of guitarist Jimmy Page, singer Robert Plant, bassist and keyboardist John Paul Jones, and drummer John Bonham. The band's heavy, guitar-driven sound has led them to be cited as one of the progenitors of heavy metal, though their unique style drew from a wide variety of influences, including blues, psychedelia, and folk music.
Document 11: Around the World Live: Around The World Live is British hard rock band Deep Purple's four DVD box-set. It was released on 19 May 2008. The box-set includes four live performances of Deep Purple World Tour (1995–2008), two full-time documentary films about the band and rare footage, including interviews, after-show parties and the band on the road, during the tour. Extensive liner notes were supplied by the author Joel McIver.
Document 12: Deep Purple: Deep Purple are an English rock band formed in Hertford in 1968. The band is 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.
Document 13: Maida Vale (album): Maida Vale: The BBC Radio One Sessions is a compilation album by Van der Graaf Generator, containing eight songs from four different recording sessions at Maida Vale Studios for BBC Radio 1 in 1971, 1975 and 1976, three of which were Peel Sessions. It was released in June 1994 on Band of Joy Records.
Document 14: List of Deep Purple band members: Deep Purple are an English hard rock band from Hertford, Hertfordshire. Originally known as Roundabout, the group formed in March 1968 featuring vocalist Rod Evans, guitarist Ritchie Blackmore, bassist Nick Simper, drummer Ian Paice and keyboardist Jon Lord. This first lineup of the band, known as Mark I, released three albums within the space of a year – "Shades of Deep Purple", "The Book of Taliesyn" and "Deep Purple" – before Evans and Simper were fired from the band at the request of Blackmore and Lord. Mark II of Deep Purple saw Ian Gillan and Roger Glover replace Evans and Simper, respectively, in the summer of 1969. This lineup of the band has since been identified as their most successful, with their next four albums reaching the top four of the UK Albums Chart, including number-one albums "Fireball" and "Machine Head".
Document 15: The Radio One Sessions (Elastica album): The Radio One Sessions is a compilation of BBC Radio One sessions recorded by Britpop group Elastica. The album is notable for the appearance of several songs not included on any other Elastica release.
ground_truth: Deep Purple