Rubber Soul sound. According to musicologist Walter Everett, some of the vocal arrangements feature the same "pantonal planing of three-part root-position triads" adopted by the Byrds, who had initially based their harmonies on the style used by the Beatles and other British Invasion bands. Riley says that the Beatles softened their music on Rubber Soul, yet by reverting to slower tempos they "draw attention to how much rhythm can do". Wide separation in the stereo image ensured that subtleties in the musical arrangements were heard; in Riley's description, this quality emphasised the "richly textured" arrangements over "everything being stirred together into one high-velocity mass". McCartney said that as part of their increased involvement in the album's production, the band members attended the mixing sessions rather than let Martin work in their absence. Until late in their career, the "primary" version of the Beatles' albums was always the monophonic mix. According to Beatles historian Bruce Spizer, Martin and the EMI engineers devoted most of their time and attention to the mono mixdowns, and generally regarded stereo as a gimmick. The band were not usually present for the stereo mixing sessions. Band dynamics While Martin recalled the sessions as having been "a very joyful time", Smith felt "something had happened between Help! and Rubber Soul", and the family atmosphere that had once characterised the relationship between the Beatles and their production team was absent. He said the project revealed the first signs of artistic conflict between Lennon and McCartney, and friction within the band as more effort was spent on perfecting each song. This also manifested in a struggle over which song should be the A-side of their next single, with Lennon insisting on "Day Tripper" (of which he was the primary writer) and publicly contradicting EMI's announcement about the upcoming release. In addition, a rift was growing between McCartney and his bandmates as he continued to abstain from taking LSD. The revelations provided by the drug had drawn Lennon and Harrison closer, and were then shared by Starr when, during the band's stay in Los Angeles that August, he had agreed to try LSD for the first time. Songs Overview Pop historian Andrew Grant Jackson describes Rubber Soul as a "synthesis of folk, rock, soul, baroque, proto-psychedelia, and the sitar". According to author Joe Harrington, the album contained the Beatles' first "psychedelic experiments", heralding the transformational effect of LSD on many