was completed in the studio. George Harrison recalled that the band had become more sophisticated about recording techniques: "Our records were progressing. We'd started out like anyone spending their first time in a studio – nervous and naive and looking for success. By this time we'd had loads of hits and were becoming more relaxed with ourselves, and more comfortable in the studio …" The band continued to develop their sound through the use of four-track recording, which EMI had introduced in 1963. They were also allowed greater freedom to experiment by the record company and by George Martin, who was gradually relinquishing his position of authority over the Beatles, as their label boss, throughout 1964, and was increasingly open to their non-standard musical ideas. The sessions resulted in the first use of a fade-in on a pop song, at the start of "Eight Days a Week", and the first time that guitar feedback had been incorporated in a pop recording, on "I Feel Fine". The band introduced new instrumentation into their basic sound, as a way to illustrate the more nuanced style adopted by Lennon in his lyric writing. This was especially evident in the range of percussion instruments, which, mainly played by Starr, included the band's first use of timpani, African hand drums and chocalho. According to MacDonald, the Beatles adopted a "less-is-more" approach in their arrangements; he cites "No Reply" as an example of the group beginning to "master the studio", whereby doubling basic parts and the use of reverb lent the performance "depth and space". As he had done since With the Beatles, Harrison continued to vary his guitar sounds, favouring a Gretsch Tennessean guitar for the first time, in addition to using his twelve-string Rickenbacker 360/12. Author André Millard describes this period as one in which the recording studio changed its identity from the Beatles' perspective, from a formal workplace into a "workshop" and "laboratory". Recording was completed on 26 October, partway through the band's four-week tour of the UK. On 18 October, the Beatles had rushed back to London from Hull, to record the A-side of their forthcoming single, "I Feel Fine", and three of the album's cover tunes (in a total of five takes). In an interview published the day before this session, Lennon admitted that the need for new original songs was "becoming a hell of a problem". The band participated in