Chopin’s Prelude 4 in e minor is an example of what can be called non-sequential chromatic voice leading. (Roig-Francoli call is non-sequential linar process.) What follows are the main features of the first twelve measures.
Implied Tonality. The piece begins on first-inversion tonic triad, and it contains no dominant-t0-tonic progressions. It ends in measure twelve on a V7, the first clear dominant harmony of e minor. The unresolved V7 and the lack of a tonic triad in root position anywhere in the excerpt means that tonality is not established. We hear the piece in e minor, but the tonality is implied.
Tonal Parenthesis. The phrase moves from the opening i6 to the ending V7 through a series of nonfunctional chords. The passage is best described as a tonal parenthesis: i6 – ( ) – V7.
Outer-voice counterpoint. The frame of the phrase is provided by the outer voices. The melody is based on a neighbor-note motive of either a half-step (B – C – B) or whole step (A – B – A). The half-step descent C – B specifically is a “sigh” motive, portraying sadness and mourning. The bass line starts with a “lament bass,” descending chromatically from G – D. Alex Ross dedicates a chapter in his new book, Listen to This, to this type of bass line and how it is found in music from the Renaissance Chacona through Classical and Romantic times, to the Blues, Led Zeppelin, and Ligeti. Just the audio examples from his book are found here with brief explanations. After the chromatic lament descent, the bass continues down to B, with several statements of the opening C – B sigh.
Linear Chromaticism. Rather than functional harmony, the voices move by linear chromaticism. Through reduction you see that at least two voices always maintain common tones between harmonies, while one or two voices move by half or whole step (usually half step). All the voices are descending throughout the passage, similar to the sigh and the lament bass.
Implied Tonal Regions. Similar to the implied tonality of e minor, secondary tonal areas of iv and III are implied through their respective dominants, unresolved.
Underlying 7 – 6 Structure. If you further reduce the passage to more essential harmonies around the opening tonic, implied iv, implied III, and the cadential movement, you find an underlying sequence of 7 – 6 suspensions. This 7 – 6 movement is sometimes ornamented with a chromatic descent.