Chamberlin and high-pitched lines on his ARP Solina synthesiser. The final addition was former King Crimson guitarist Robert Fripp, who was recruited at Eno's suggestion. Receiving little guidance from Bowie, he cut three takes all based on feedback loops. For each take, Fripp marked different spots on the studio floor with tape and played a different note in each spot, such as A at four feet from his amp and G at three feet, all while his guitar was fed through Eno's EMS Synthi. When mixing the backing track, Visconti merged Fripp's takes onto one track, creating what he called "a dreamy, wailing quality". He buried Davis's kick drum, finding it "seemed to plod" the track and becoming "more energetic without it", and elevated Murray's bassline, which Alomar augmented on guitar in a higher register. An intended horn section was replaced with a synthesised brass line by the Chamberlin, while the bassline replaced the originally planned string section. With percussion, Visconti added tambourine and struck an empty tape canister with a drumstick as a placement for a cowbell. Vocals Similar to Low, Bowie neglected to write lyrics until all but he and Visconti had departed. As such, the backing track for Heroes sat untouched for many weeks and for a time was rumoured it would remain an instrumental. On one day, Bowie requested Visconti leave him alone in the studio to focus on writing lyrics. As he stared outside the studio window, he witnessed Visconti and singer Antonia Maass kiss in close proximity to the Berlin Wall, which he used as the basis for the lyric. Bowie initially claimed that the lyric was based on an anonymous young couple, but Visconti, who was married to Mary Hopkin at the time, contended that Bowie was protecting him and his affair with Maass. Bowie later confirmed the story in 2003, over two decades after Visconti and Hopkin's eventual divorce: "Tony was married at the time, and I could never say who it was. I think possibly the marriage was in the last few months, and it was very touching because I could see that Tony was very much in love with this girl, and it was that relationship which sort of motivated the song." Additionally, he improvised lyrics while standing at the microphone after witnessing Pop use the same method during the making of The Idiot (1977) and Lust for Life. To