Musical evolution

The Beatles' constant demands to create new sounds on every new recording, combined with George Martin's arranging abilities and the studio expertise of EMI staff engineers such as Norman Smith, Ken Townshend and Geoff Emerick, all played significant parts in the innovative sounds of the albums Rubber Soul (1965), Revolver (1966) and Sgt. Pepper's Lonely Hearts Club Band (1967).

The Beatles continued to absorb influences long after their initial success, often finding new musical and lyrical avenues by listening to their contemporaries. Among those influences were Bob Dylan, who influenced songs such as "You've Got to Hide Your Love Away" and "Norwegian Wood (This Bird Has Flown)".^[89] Other contemporary influences included the Byrds and the Beach Boys, whose album Pet Sounds was a favourite of McCartney's.^[90]

Along with studio tricks such as sound effects, unconventional microphone placements, tape loops, double tracking and vari-speed recording, The Beatles began to augment their recordings with instruments that were unconventional for rock music at the time. These included string and brass ensembles as well as Indian instruments such as the sitar as in "Norwegian Wood (This Bird Has Flown)" and the swarmandel as in "Strawberry Fields Forever". They also used early electronic instruments such as the Mellotron, with which McCartney supplied the flute voices on the intro to "Strawberry Fields Forever", and the ondioline, an electronic keyboard that created the unusual oboe-like sound on "Baby You're a Rich Man".

Beginning with the use of a string quartet (arranged by George Martin with input from McCartney) on "Yesterday" in 1965, The Beatles pioneered a modern form of art song, exemplified by the double-quartet string arrangement on "Eleanor Rigby" (1966), "Here, There and Everywhere" (1966) and "She's Leaving Home" (1967). A televised performance of Bach's Brandenburg Concerto No. 2 directly inspired McCartney's use of a piccolo trumpet on the arrangement of "Penny Lane". The Beatles moved towards psychedelia with "Rain" and "Tomorrow Never Knows" from 1966, and "Lucy in the Sky with Diamonds", "Strawberry Fields Forever" and "I Am the Walrus" from 1967.