Sgt. Pepper's Lonely Hearts Club Band "Being for the Benefit of Mr. Kite!" and "A Day in the Life". Producer George Martin and engineer Geoff Emerick helped realise the group's ideas by approaching the studio as an instrument, applying orchestral overdubs, sound effects and other methods of tape manipulation. Recording was completed on 21 April 1967. The cover, depicting the Beatles posing in front of a tableau of celebrities and historical figures, was designed by the British pop artists Peter Blake and Jann Haworth. "Sgt. Pepper" is regarded by musicologists as an early concept album that advanced the use of extended form in popular music while
Sgt. Pepper's Lonely Hearts Club Band peers", he continues, "what was revolutionary was the sonic carpet that enveloped the ears and sent the listener spinning into other realms." Stephen Thomas Erlewine of AllMusic considers the album to be a refinement of "Revolver"s "previously unheard-of level of sophistication and fearless experimentation" and a work that combines a wide range of musical styles yet "Not once does the diversity seem forced". He concludes: "After "Sgt. Pepper", there were no rules to follow – rock and pop bands could try anything, for better or worse." In 1987, Anthony DeCurtis of "Rolling Stone" described "Sgt. Pepper" as the album that