To alleviate tensions within the band and improve the quality of their live sound, Harrison invited keyboardist Billy Preston to participate in the last nine days of sessions. Preston received label billing on the "Get Back" single – the only musician ever to receive that acknowledgment on an official Beatles release. After the rehearsals, the band could not agree on a location to film a concert, rejecting several ideas, including a boat at sea, a lunatic asylum, the Tunisian desert, and the Colosseum. Ultimately, what would be their final live performance was filmed on the rooftop of the Apple Corps building at 3 Savile Row, London, on 30 January 1969. Five weeks later, engineer Glyn Johns, whom Lewisohn describes as "Get Back"s "uncredited producer", began work assembling an album, given "free rein" as the band "all but washed their hands of the entire project".