I sometimes think the classical record industry would collapse if it weren’t for the Goldberg Variations. Every month brings more recordings of Bach’s monumental, compact and rhapsodic keyboard masterpiece. And that’s impressive, given that nowhere else does the composer demand such sustained technical brilliance from the performer, who must execute dizzying scales and trills that wouldn’t sound out of place in one of Liszt’s fantasies. If the Goldberg Variations are an ordeal for harpsichordists, they’re a bloody nightmare for pianists, because they have to tackle music written for two manuals on just one. Their fingers tumble perilously over each other; it looks a bit like high-speed knitting. When the 22-year-old Canadian prodigy Glenn Gould — already dosed up on the barbiturates that would shorten his life —shuffled into Columbia’s studios to record the Goldbergs in 1955, there wasn’t a single piano performance in the catalogue.