Discussion of the prelude and fugue shows up after the break.
Prelude (start of video)
This has a mid-tempo feel to it but is like a brisk walk (quarter equals 132 bpm). After a single measure introduction the lilting, rising gesture of B, C, D, E in quarter notes appears in measure 2, followed by a small leap to G and a descent from G through F and E in staggered and repeating rhythms. That this central motto begins on a leading tone rather than a tonic is the crucial element of this motto throughout the prelude, because it allows Koshkin to introduce mercurial modal mutations by manipulating how this motto is presented in terms of modal mutation on one hand and in terms of harmonic juxtaposition on the other.
No sooner has this opening motto (five measures) in C major been presented, Koshkin presents a new form of it in E flat major. Even this E flat major phrase mutates into parallel minor in enharmonic spelling. Though this is a little prelude there's a dramatic arc at play. The third phrase on the motto turns it into a two-measure sequence of quarter notes that brings us back to C, but C minor. Koshkin's used his second phrase on E flat to move quickly back to the tonic key but in its parallel minor, building up to a climax that has us in the "wrong" key for a prelude in C major, the climax of the movement in terms of being the literal high point of the melodic journey and by being in C minor rather than major. Koshkin makes a swift yet gentle descent through passage work that evokes Bach's Bourree from BWV 996 without actually quoting it.
As he continues to wind down with descending melodic activity Koshkin has some interesting harmonic pivots I'd write more about if I were writing, say, a treatise. Instead I'm going to note that he wraps things up with an augmentation (in half notes) of his initial melodic motto and ends with a semi-half cadence that prepares the way for the fugue.
Fugue (starts at 1:22)
As fugues go this subject has an unusually large ambit, a compound fifth. The fugue is what is known as a "white" fugue, a fugue in C major in which no accidentals or chromatic alterations occur anywhere in the piece. Given how unstable and prone to modal mutation the prelude was, composing a "white" fugue could seem as though it can't effectively be "preluded" by what we've just heard. But there's a unifying element, you can see it in the score and hear it, the prelude and the fugal subject are defined by mottos that lean on the leading tone and third degree of the tonic chord. This allows for even the "white" fugue to retain a faintly jazzy air by having a subject that outlines a C major seventh chord in its opening two measures.
The fugue has three voices (tenor, alto, soprano for choral thinking). The entrances can be described as follows
1. Subject enters in alto on the tonic
2. Answer enters in tenor on the dominant
3. Subject reprised in soprano on the tonic.
There isn't exactly a countersubject but if there is one then the countersubject candidate in the initial voice is a gesture that is freely inverted when it appears under the third entrance of the subject. Since countersubjects can appear either in prime or inversion form that's worth noting as we start blogging through all of these preludes and fugues.
Since it would be difficult to try describing episodes in fugues even to people already familiar with fugal writing I'll stick to commenting about something that's easier to hear and identify in a score. There are a number of middle entries in this fugue. Middle entries are moments in the fugue in which the subject is presented in its full (or fully identifiable) form before proceeding to episode development. The first appears at measure 44 and is in E minor.
The second middle entry is in G major and is at measure 48. What makes this middle entry interesting is the subject is presented in canon against itself. The episodic material is rather extensive moving along from here and the next middle entry is in F at measure 60, followed by another canonic middle entry at measure 62 and in this case the canonic relationship is switched. In the first canonic middle entry the lower voice starts first and is followed by the upper, while in this second canonic middle entry the upper voice begins and the lower voices responds.
The climax of the fugue could arguably be at measure 64, where the subject in the alto is supported by the tenor (i.e. bass) and is answered in the soprano by a free inversion of the subject as a quasi-stretto passage where the subject is answered by an inversion.
As fugues go this one is elegant and simple. Starting with a "white" fugue has precedent enough in the Shostakovich cycle and Koshkin has indicated that Shostakovich and Stravinsky are among his inspirations. The juxtaposition of a harmonically violent prelude and a gentle "white" fugue is a nice way to start this cycle.