It Was 40 Years Ago Today|PARADE Magazine: "This week marks the 40th anniversary of the Beatles’ completion of Sgt. Pepper’s Lonely Hearts Club Band, a tour de force that elevated the rock album to art form and taught generations of bands to play.
The 13 tracks on Sgt. Pepper’s were conceived in a magical span of 700 hours over five months. The Beatles began recording on Dec. 6, 1966, and finished the album on April 21, 1967, when they created the final track, an avant-garde seconds-long pastiche of sounds—including a high-pitched tone inaudible to humans put there solely to annoy your dog—that was later dubbed “Inner Groove” for its bizarre placement within the concentric circles of the LP."