More overdubs were added on 21 June followed by final mixing in stereo. The stereo master was completed on 25 June when it was shortened by 53 seconds. Although other songs on the album were separately remixed for the mono version, the complexity of "Revolution 9" necessitated making the mono mix a direct reduction of the final stereo master. McCartney had been out of the country when "Revolution 9" was assembled and mixed; he was unimpressed when he first heard the finished track, and later tried to persuade Lennon to drop his insistence that it be included on the album. Lennon said that the final editing was done by himself and Ono alone.