Julien describes "Sgt. Pepper" as a "masterpiece of British psychedelia" and says that it represents the "epitome of the transformation of the recording studio into a compositional tool", marking the moment when "popular music entered the era of phonographic composition". Many acts copied the album's psychedelic sounds and imitated its production techniques, resulting in a rapid expansion of the producer's role. In this regard, Lennon and McCartney complained that Martin had received too much attention for his part in the album's creation, so beginning a feeling of resentment by the Beatles towards their longtime producer.