Task: Question Answering
Input (English): Passage: Almost as soon as they returned home, the Beatles faced a fierce backlash from US religious and social conservatives (as well as the Ku Klux Klan) over a comment Lennon had made in a March interview with British reporter Maureen Cleave. "Christianity will go," Lennon had said. "It will vanish and shrink. I needn't argue about that; I'm right and I will be proved right. ... Jesus was alright but his disciples were thick and ordinary. It's them twisting it that ruins it for me." The comment went virtually unnoticed in England, but when US teenage fan magazine Datebook printed it five months later – on the eve of the group's August US tour – it sparked a controversy with Christians in the American "Bible Belt". The Vatican issued a protest, and bans on Beatles' records were imposed by Spanish and Dutch stations and South Africa's national broadcasting service. Epstein accused Datebook of having taken Lennon's words out of context; at a press conference Lennon pointed out, "If I'd said television was more popular than Jesus, I might have got away with it." Lennon claimed that he was referring to how other people viewed their success, but at the prompting of reporters, he concluded: "If you want me to apologise, if that will make you happy, then okay, I'm sorry."As preparations were made for the US tour, 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 by Vox for them as they moved into larger venues in 1964, but 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.
Rubber Soul had marked a major step forward; Revolver, released in August 1966 a week before the Beatles' final tour, marked another. Pitchfork's Scott Plagenhoef identifies it as "the sound of a band growing into supreme confidence" and "redefining what was expected from popular music". Revolver featured sophisticated songwriting, studio experimentation, and a greatly expanded repertoire of musical styles, ranging from innovative classical string arrangements to psychedelic rock. Abandoning the customary group photograph, its cover – designed by Klaus Voormann, a friend of the band since their Hamburg days – "was a stark, arty, black-and-white collage that caricatured the Beatles in a pen-and-ink style beholden to Aubrey Beardsley", in Gould's description. 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 1966. 
Question: What were the Beatles competing with to make their music heard on tour?
Output (English): the volume of sound generated by screaming fans.