On a recent long-haul flight, I experimented on myself. The in-flight entertainment system had all Chopin’s Piano Preludes in sequence. These are arranged in major/minor key pairs going from C major through the sharp keys, adding a sharp at a time. Then he shifts to the most complex flat keys and sequentially removing a flat at a time, ending with a tirade in D minor, the minor key with one flat. How would I hear them now? And in sequence?

From C major to A major, the Preludes all sounded in the correct key. When I arrived at the very busy F sharp minor (on the score it looks as if Chopin flicked his pen at the manuscript producing dozens of dots in each bar!), a sharpening of the pitch began. The sonorous E major Prelude was more like light weight F major in timbre but not quite. The brief C sharp minor Prelude definitely ended in D minor to my ears. The next in the sequence was in B major, but by now things had shifted completely and from this one – now sounding in C major through the next 4 preludes (including the famous D flat major Raindrop Prelude with its drumming C sharp minor central section which for me had all the dialectical character of C minor), we were a semitone up. As we descended’ through the flat keys (if the Prelude sequence is conceived as a great arch), there was a section of ‘sharpish, not yet truly sounding in the flat keys’ until the true C minor of that most famous of Preludes appeared. As the heavy chords began, there I was back ‘in key’, there I stayed through to the resonant deep satisfying D’s of the final D minor Prelude.