Titled 'As evening falls,' this piece likely aims to evoke the mood and atmosphere of twilight, perhaps with a sense of calm, reflection, or gentle melancholy. Its musical distinctiveness would be in its atmospheric qualities and expressive melodic lines.
Emphasize smooth transitions and a rich, resonant tone to create the desired evening ambiance.
Au soir tombant (Op.39) is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
Au soir tombant (Op.39) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.