Colin Greenwood on Alex Ross

Colin Greenwood and Alex Ross, the New Yorker's music critic, talk about taste on a stage at the Southbank Centre, during the festival built on Ross's book The Rest Is Noise. Ross's London publisher knew Colin and passed on his America Online address, and the two have since spent hours in Colin's kitchen playing each other music. Jonny, “more shy than I am”, Colin says, stayed at home practising the ondes Martenot and sent a playlist that opens with Bartók's First Piano Concerto.

Colin grew up in an army household in Germany, where the classical records came out on Sunday. At school the director of music, Terence James, was the band's champion. When the headmaster billed them £60 for rehearsing on Sundays, James stormed into the headmaster's office and tore the bill up on the desk. Colin plays “The Mango Vendor” by Nina and Frederik, the slightly melancholy 1960s song the brothers heard on Sunday mornings. Ross calls it the long-lost Rosetta Stone of Radiohead, and says Colin meant to play it on 6 Music and lost his nerve.

Kid A, as Colin tells it, was a dialogue between Thom Yorke, who was listening to Warp records and wanted to move away from guitars, and Jonny, who answered him. Yorke and Nigel Godrich recorded the album's first song, “Everything in Its Right Place”, in a huge haunted house at Batsford in the Gloucestershire countryside. Back in the day, watching string players at Abbey Road do the crossword and answer their phones while they played irked Jonny, and made him keen to keep cliché pop strings out of Radiohead's music. Junior Walker's “Shotgun”, built on one chord that never shifts, holds a lot of what Colin tries to do as a bass player, in its repetition and the way it builds.

EMI lent the band about £30,000 against their advance for a rusty white van and a drum kit, and let them learn in front of six people a night; that middle ground has worn away. His ten-year-old plays him tracks made of GarageBand loops, and Colin thinks of himself and Jonny at that age, on recorder and guitar. Talking music to a room of strangers, he says, is “far, far less terrifying than being on a Radiohead tour bus and playing something I like to my four friends in the band”.