Later came precursors of modern classical music. Érik Satie was a key member of the early-20th-century Parisian avant-garde, best known for his ''Gymnopédies''. Francis Poulenc's best known works are his piano suite ''Trois mouvements perpétuels'' (1919), the ballet ''Les biches'' (1923), the ''Concert champêtre'' (1928) for harpsichord and orchestra, the opera ''Dialogues des Carmélites'' (1957) and the ''Gloria'' (1959) for soprano, choir and orchestra. Maurice Ravel and Claude Debussy are the most prominent figures associated with Impressionist music. Debussy was among the most influential composers of the late 19th and early 20th centuries, and his use of non-traditional scales and chromaticism influenced many composers who followed. Debussy's music is noted for its sensory content and frequent usage of atonality. The two composers invented new musical forms and new sounds. Ravel's piano compositions, such as ''Jeux d'eau'', ''Miroirs'', ''Le tombeau de Couperin'' and ''Gaspard de la nuit'', demand considerable virtuosity. His mastery of orchestration is evident in the ''Rapsodie espagnole'', ''Daphnis et Chloé'', his arrangement of Modest Mussorgsky's ''Pictures at an Exhibition'' and his orchestral work ''Boléro'' (1928). More recently, the middle of the 20th century, Maurice Ohana, Pierre Schaeffer and Pierre Boulez contributed to the evolutions of contemporary classical music.