the previously recorded tracks except the Hammond organ part. Harrison then recorded two tracks of vocal, one of which included more trumpet from McCartney and further vocalised sounds, while the final track was filled with timpani, Mellotron, piano and more organ. The presence of Harrison's original Hammond part on both of the tapes ensured that the instrument had a more substantial sound in the mix. The Beatles performed many of the overdubs in a haphazard manner. Tom Maginnis of AllMusic describes the completed track as "heavily steeped in the psychedelic sounds of the period, using liberal amounts of loose instrumentation", particularly "chaotic bursts of trumpet". According to Pollack, these additions constitute a "noise track", which further heightens the theme of discordance, and is used to fill the song's instrumental sections, becoming especially prominent during the outro. With its inclusion of random sounds and spoken voices, Inglis cites the sound collage effect as a precedent for Lennon's 1968 avant-garde track "Revolution 9" and an early example of electronic music. Mixing On 21 April, the Beatles completed a mono mix of the song for its inclusion in Yellow Submarine. Due to the difficulty in getting the two 4-track machines to play at exactly the same time, attempts at creating a stereo equivalent were abandoned. In October 1968, while preparing the Yellow Submarine soundtrack album for release, EMI's engineers created a duophonic (or mock-stereo) mix of "Only a Northern Song" from the mono mix. The monaural version of the album, which was originally available only in the UK, similarly used a suboptimal version of the recording. In this case, as with the three other new songs presented to United Artists, the engineers combined the two channels from the duophonic mix, rather than use the true mono mix from April 1967. Appearance in Yellow Submarine film The Beatles had minimal involvement in the making of Yellow Submarine, leaving the production to Brodax's company King Features Syndicate. The film-makers drew heavily on the Sgt. Pepper concept, the Beatles' association with Liverpool, and other aspects of their public image. While the project's art design was carried out by a team led by Heinz Edelmann, sequences such as "Eleanor Rigby" and "Only a Northern Song" were created by outside animators, ensuring stylistic variation across the film. "Only a Northern Song" plays over a scene when the yellow submarine travels through the Sea of Science, during the Beatles'