Étude in C♯ minor "Torrent" (Op.10 No.4) , F. Chopin

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Étude Op. 10, No. 4 in C♯ minor, known as the Torrent étude, is a study for solo piano composed by Frédéric Chopin in 1830. This study, a very fast Presto con fuoco, features continuous sixteenth notes (semiquavers), in perpetuum mobile fashion involving both hands.
Like all of Chopin's other études, this work is in ABA form though the B section does not represent a contrasting and independent middle section in the manner of a trio. The entire piece is based on the same semiquaver motif, which springs from its opening strong sforzato accent to rapidly increase its volume and compass until ending abruptly on a strong sforzato climax. The manner in which the motif is developed, especially the 4-bar alternations of left and right hand in the rendition of the theme, can be compared to certain Bach preludes, or to the gigue of J. S. Bach's English Suite No. 6.
This Study was written to develop perfect equality of the two hands. Even though Chopin had always required a lot of technique for the left hand in his compositions, he had always composed pieces in which the tasks of the hands were very distinct; in this Study, both from a technical and strictly musical point of view, the realization is absolutely identical for the two hands.
The Etude in C sharp minor is a bravura piece, an uninterrupted exercise, like a perpetuum mobile where the two hands meet, reach each other, fight. It must be performed with a very fast movement which makes the execution of the semiquaver chains difficult; it is also essential to possess absolute technical mastery, the succession of semiquavers does not in fact allow for classic fingering and also requires the use of the thumb on the black keys, which is completely unusual; in this way any crossing of fingers is eliminated, allowing for considerable speed of execution. The difficulties for the pianist are considerable, from the attack of great impetuosity, to the rapid alternation of the positions of the hands, the performer must then take care not to lose the thread of the melodic lines that pass from one voice to another.
From the autograph writing at the end of the score of Study No.3, Attack the Presto with fire , i.e. the beginning of Study n. 4, it can be assumed that Chopin designed the Studies to be performed two by two; the particular note was made following the writing of the pieces, as the composition of Studio n. 4 previous to n. 3. The effect is in fact grandiose when the execution is proposed without interruption; the contrast between the two romantic songs, one lyrical and melodious and the other passionate and overwhelming, is certainly effective.
The study is classified under the category "speed and lightness". The procedure of transferring the semiquaver figuration from one hand to the other, common in Bach but rare in Chopin, "makes great demands on the left hand." Chopin [in other works] rarely treats the left hand "as if it were a second right hand."