 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".