

The melody has a nursery-rhyme-like simplicity, aside from a few ninths and thirteenths on the V chord. The first eight bars of the prelude alternate back and forth between the I and V chords in D-flat major, Db and Ab7. So you can see why Chopin would rather write in C-sharp minor. Conversely, C-sharp minor has only four sharps, whereas D-flat minor has six flats and a double flat–it shares the same horrifying key signature as F-flat major. D-flat major has five flats, whereas C-sharp major has seven sharps, so D-flat major is less annoying to write and read. The reason has nothing to do with how the music sounds it’s a practical issue with key signatures. But why didn’t Chopin write the middle part in D-flat minor? Or write the first and last parts in C-sharp major? Either way, it would sound exactly the same.

Switching between major and minor keys on the same root is a common compositional technique–you can hear it in the Bach Chaconne too. I was confused when I read that the first and last sections of the prelude are in D-flat major, but that the middle section is in C-sharp minor. Rather than trying to figure out what the pedal “represents,” it makes more sense to me to understand the prelude as being about the idea of pedal point. I mean, if you could verbally convey the meaning of music, you wouldn’t need the music. Maybe so, but the likeliest explanation is that the pedal point just sounds good, and that it evokes too many different feelings and associations to be neatly expressible by language. Another theory is that Chopin was trying to symbolize the tolling of a bell to evoke death coming for us all. George Sand told a story about Chopin writing the piece on a rainy day, or in response to a rainy day, but that is probably not true. It’s a gentle pulse in the first and last sections, but it builds to a relentless pounding in the middle section. The most conspicuous feature of this prelude is the near-constant A-flat/G-sharp pedal point. Chopin’s actual title of this piece is “12 Préludes, Opus 28 Number 15 in D-Flat Major.” That’s not very memorable, though, so von Bülow’s name stuck. The names were given later by a fan named Hans von Bülow. Chopin didn’t title the piece “Raindrop,” nor did he give catchy nicknames to any of his other preludes.
