1966, a week before the Beatles' final tour, Revolver marked another artistic step forward for the group. The album featured sophisticated songwriting, studio experimentation, and a greatly expanded repertoire of musical styles, ranging from innovative classical string arrangements to psychedelia. Abandoning the customary group photograph, its Aubrey Beardsley-inspired cover – designed by Klaus Voormann, a friend of the band since their Hamburg days – was a monochrome collage and line drawing caricature of the group. The album was preceded by the single "Paperback Writer", backed by "Rain". Short promotional films were made for both songs; described by cultural historian Saul Austerlitz as "among the first true music videos", they aired on The Ed Sullivan Show and Top of the Pops in June. Among the experimental songs on Revolver was "Tomorrow Never Knows", the lyrics for which Lennon drew from Timothy Leary's The Psychedelic Experience: A Manual Based on the Tibetan Book of the Dead. Its creation involved eight tape decks distributed about the EMI building, each staffed by an engineer or band member, who randomly varied the movement of a tape loop while Martin created a composite recording by sampling the incoming data. McCartney's "Eleanor Rigby" made prominent use of a string octet; Gould describes it as "a true hybrid, conforming to no recognisable style or genre of song". Harrison's emergence as a songwriter was reflected in three of his compositions appearing on the record. Among these, "Taxman", which opened the album, marked the first example of the Beatles making a political statement through their music. In 2020, Rolling Stone ranked Revolver at #11 on their list of "The 500 Greatest Albums of All Time". As preparations were made for a tour of the US, the Beatles knew that their music would hardly be heard. Having originally used Vox AC30 amplifiers, they later acquired more powerful 100-watt amplifiers, specially designed for them by Vox, as they moved into larger venues in 1964; however, these were still inadequate. Struggling to compete with the volume of sound generated by screaming fans, the band had grown increasingly bored with the routine of performing live. Recognising that their shows were no longer about the music, they decided to make the August tour their last. The band performed none of their new songs on the tour. In Chris Ingham's description, they were very much "studio creations ... and there was no way a four-piece rock