This piece is one of the Études from the work 'Three Concert Études' by Franz Liszt. Liszt was a virtuoso pianist, and the goal of these works is twofold: they are etudes, i.e. for study purposes and improving ones technique, but also melodically beautiful enough to be played as concert works.
As most of the works of Liszt the pieces expect a high technical demand from the player. Un Sospiro (Italian for 'a sigh') is the third etude of the concert etudes and a study in crossing hands, playing a simple melody with alternating hands, and arpeggios. It is also a study in the way hands should affect the melody with its many accentuations, or phrasing with alternating hands. The melody is quite dramatic, almost impressionistic, radically changing in dynamics at times, and has inspired many listeners. The étude has been considered by many pianists as one of the most beautiful piano pieces ever composed. Liszt kept the étude in his repertoire until his final years.
Un sospiro consists of a flowing background superimposed by a simple melody written in the third staff. This third staff—an additional treble staff—is written with the direction to the performer that notes with the stem up are for the right hand and notes with the stem down are for the left hand. The background alternates between the left and right hands in such a way that for most of the piece, while the left hand is playing the harmony, the right hand is playing the melody, and vice versa, with the left hand crossing over the right as it continues the melody for a short while before regressing again. There are also small cadenza sections requiring delicate fingerwork throughout the middle section of the piece.
Towards the end, after the main climax of the piece, both hands are needed to cross in an even more complex pattern. Since there are so many notes to be played rapidly and they are too far away from other clusters of notes that must be played as well, the hands are required to cross multiple times to reach dramatic notes near the end of the piece on the last page.
Sheet music from IMSLP.org
