HARMONIC RHYTHM

The next figure shows the beginning of Chopin's Prelude No. 9 in E major. We see that there are a lot of chords in these five measures. This is often the case when the tempo of a composition is slow. In fact, the frequency of change in chords is often a good measure to how fast or slow the composition should be played. When chords change frequently and we play the composition at a fast tempo, a listener will not be able to comprehend the music well. The same is true when chords change infrequently and we play the composition at a slow tempo. It is quite like talking too fast or too slow. 

A harmonic rhythm is defined as the rhythm of chord changes. In this prelude, the harmonic rhythm is mostly equal to the rhythmic value of a single quarter note. That is, one chord change happens during a single quarter note.