Duo-Sonata, like many of the other works on this album, was commissioned by Emilie Fend and Andreas Hermanski. In the words of the composer, the piece 'conforms to the Classical form concept. Not only does the first movement conform with the sonata-allegro form, but it also keeps the four movements of many works from the early 19th century.' If the listeners can easily recognize such a formal plan, they might also experience a sense of slight contrast with the qualities of Sierra's musical language. This is, as a matter of fact, quite modernist, yet expressive - all managed within a very balanced and thought-out approach to writing.