Noctave
The piece
It was not Chopin who called this prelude the “Raindrop”. The nickname comes from a repeated note that runs through almost the whole piece: an A-flat, in steady eighth notes, beneath the melody of the first section. In the middle, the key moves to C-sharp minor, the same note is now written G-sharp, and the mood darkens: low chords support a long crescendo that leads to two fortissimo peaks, before the opening theme returns, calmer.
The repeated note changes hands: in the left hand at first, it moves to the right hand in the central section, where it is doubled at the octave, for more than 160 attacks in octaves. It should stay soft and even, like a background, even when everything swells around it: loose wrist, never hammered. Beneath it, the left hand sings in the bass; give it the foreground. The key signature switches from five flats to four sharps, then back. The central crescendo is long: pace it so you still have something left for the fortissimo.