David Dubal is back on radio, spinning his musical comparisons. “While much of classical radio these days seems to consist of little more than DJs dispensing tuneful wallpaper, on any given Wednesday evening, “Reflections From the Keyboard” invites the listener to deepen his or her musical experience. “Where else, within a six-minute span, can you hear a movement of Schumann’s ‘Carnival’ played by Rachmaninoff, Cortot, Hess, Arrau, Godowsky and Michelangeli?”