The Beatles (album) stereo only. In the UK, the following album, "Yellow Submarine", was the last to be shipped in mono. The mono version of "The Beatles" was made available worldwide on 9 September 2009, as part of "The Beatles in Mono" CD boxed set. A reissue of the original mono LP was released worldwide in September 2014. The album's sleeve was designed by pop artist Richard Hamilton, in collaboration with McCartney. Hamilton's design was in stark contrast to Peter Blake's vivid cover art for "Sgt. Pepper's Lonely Hearts Club Band", and consisted of a plain white sleeve. The band's name, in Helvetica,
Sgt. Pepper's Lonely Hearts Club Band of Invention has also been cited as having influenced "Sgt. Pepper". According to the author Philip Norman, during the "Sgt. Pepper" recording sessions McCartney repeatedly stated: "This is our "Freak Out!"" The music journalist Chet Flippo states that McCartney was inspired to record a concept album after hearing "Freak Out!" Martin recalled that "Sgt. Pepper" "grew naturally out of "Revolver"", marking "an era of almost continuous technological experimentation". According to Geoff Emerick, the Beatles' recording engineer, the "major difference" between the two albums was that, with "Sgt. Pepper", there was no absolute deadline for completion. Sessions began on 24 November