A Chromatic-Like Prelude by Chopin
Chopin wrote in a variety of ways, and Prelude No. 21 is just one those flexibility examples. The interesting thing about this prelude is the chromatic approach in the left hand. The melody is pretty straightforward, not much movement, soaring above the accompaniment. The left hand is where the prelude happens. A repeating pattern that is based off the chromatic scale. To be fair, it is not entirely chromatic, Chopin does use whole steps, and I would say the chromatic approach is very selective. He only uses it when it makes sense in the harmony, otherwise he just sticks to a regular scale. One example of this is measure 1: here Chopin uses only 2 half steps. But in measures 5 and 6 he uses 4 half steps each. Measure 13, 14, and 15 is another interesting example. Chopin decides to use chromatic progressions in both hands, temporarily halting the melody. (or maybe transitioning the melody into the chromatic prelude theme). Measure 33 is another interesting spot. The melody remains in the right hand, but now the right hand starts assisting the left hand in the prelude pattern. I remember typing up measure 41 - 44. There was so much different fingerings for each part. It was very time consuming.
Now, lets talk a little bit about my students learning this piece. First of all, I think this piece should be taught only to the most advanced students, and even then only if they are studying all the Chopin etudes. Secondly, the most important part of learning this prelude is to understand the chromatic concept. Start at measure 41 - 44. I know no one wants to start in the middle, but if you starting teaching or learning the piece there, you will understand the whole direction of the piece and it will be much easier for you to learn everything. Once those hard measure feel comfortable, I'm sure the rest of the prelude will be easy enough. Enjoy!