A single gesture, rhythm harmonic progression, melody, or the like, is often the compositional basis for an entire piece. Maximizing this material’s potential is what leads to new discoveries and subsequent developments in the music. In this particular case, all of the above mentioned aspects are integrated into a single idea: an ostinato that circles around itself in contrary motion while emphasizing the outer pitches and articulating a specific harmony—a seven-note chord that is divided into two tertian sonorities: a D major triad in the right hand and a Cm7 in the left. This ostinato appears at the beginning of the piece—emerging from an explosive opening gesture sustained by the piano’s incredible resonance—and returns at the denouement, gradually building to a climactic figuration at the outer limits of the piano’s register. The rhythmically persistent nature of the ostinato is never absent (except for the middle section, which develops the harmony of the ostinato) and yet, never overtly prominent, as changes in texture and character are frequently employed.
The word “Ambitus” is a Latin term literally meaning “the going round,” which was used in Medieval music to describe the range of scale degrees attributed to a particular mode in Gregorian chant. It may also refer to the range of a vocal or instrumental part.
Both aspects (the “going round” and “range”) figure prominently in the music. The entire and immense registral range of the piano is exploited throughout the piece and the repetitious/circular ostinato figures contain the range within a smaller frame, emphasizing the music’s “going round.”