Barely discernible, Air on the G String sounds from after-party windows of May: candelight, firelight. Clonks and imperfects add to the feel. The Air’s temperament, never devolving into melancholy, is discerned through scratches and aged bumps of 78. At 27 the thread tug-clicks inside crappy cassettes, slowing to a whine before massing in brown tape clumps. Bach’s mathematical manner rarely obtrudes on his verve, though perfection’s taken to new extremes on compact discs of scintillating sameness. Thus habituated, musicians online outgrow compactness. Elongated ambience and you-tuba versions intrude. An artist performs the Air with a large ensemble of filmy g-strings.