The theme, which is basically 16 measures long, is a very small rounded, continuous binary form. The A section is a parallel, open period consisting of two phrases that are separated by a half cadence in D major, symmetrical (four measures long), and modulate to A major, ending with a PAC in that key. I heard it as a modulation to A major because there was a strong emphasis on G# for two measures leading up to measure 8. The B section is simply a four measure phrase. However, the tonality of this phrase is different enough from the first two - it suggests A major, then E, then D (m. 9) during its brief developmental phase, before transitioning back to the original tonality with a half cadence in D major (m. 12). Rounding begins with the return of A in measure 13, this time finishing with a PAC in D major.
Now to discuss the varied elements of each variation:
The most obvious change is rhythmic - the eight note pulse is lost to the eigth note triplet. The structure and harmony are kept. The melody is disguised within the winding triplets, though it's still very present.
There are more changes here. One is in the dynamics - this variation alternates between piano and forte much more often than the theme. The density and texture change as well - the hands often play alone, giving the variation a contrapuntal sound. The structure and harmony are kept, but the melody is very obscured in a sort of call and response between the hands.
**Just realized there are 12 variations, so I will be commenting less and more in an outline format on the following 10, focusing on the most significant changes.
-Rhythm change: sixteenth not becomes basic pulse.
-Timbre change: piece beomes much more rough, especially because of the descending parallel
octaves in the left hand.
-Texture change: the fast moving notes are now in the bass, whereas the right hand plays slower.
-Original structure and harmony are still present, but the melody is basically impossible to pick out.
-Rhythm change: eight note is basic pulse.
-Tempo change: much slower, calmer.
-Timbre chagne: brash sound of chords in right hand of var. 4 is replaced by a smooth, relaxed sound.
-Rhythm change: back to the 16th note as basic pulse.
-Register change: left hand moves lower than var. 5, right hand at times is higher. Basically, the middle range isn't the center of activity like var. 5.
-Texture change: unison chords are replaced by fast arpeggiations.
-Tempo change: much faster
-Tempo change: slower.
-Dynamic change: softer, calmer mood.
-Tonality change: the piece changes from D major to d minor.
-Timbre chage: the excited, flighty sound of var. 6 is replaced by somber, mellow sound.
-Tonality change: back to D major.
-Tempo change: quicker again.
-Timbre change: back to a happier, bright sound.
-Texture change: now a contrapuntal texture - var. 7 had one melodic line over accompaniment.
-Dynamic change: louder.
-Overall, similar in many ways to var. 8.
-Dynamic change: much more contrast, sudden.
-Rhythmic change: 16th note is very present.
-Texture change: Octaves are split into oscillating 16ths.
-Meter change: now in common time, not cut.
-Tempo change: slower.
-Timbre change: much more mellow, no longer bright and excited.
-Texture change: back to a solo melodic line with accompaniment rather than a contrapuntal sound where both hands play parts of the melody.
-Form and structure are varied in that A and B are not just repeated, but the whole thing is written out.
-Meter change: in 3/4 now - first compound feel of the entire piece.
-Timbre change: back to excited, bright.
-Rhythm change: 16th note is back.
-Dynamic change: louder in general, with more sudden contrasts.
The structure and harmony basically remained constant throughout the entire piece, though the melody was basically lost in all the variations. Bits and pieces of the original could be heard later in the piece, but other than that it was changed significantly.