Complex sentence: He worked at the Opéra and the Opéra-Comique in Paris before founding his own orchestra, the "Orchestre des Concerts Straram", in 1925, which was considered by some to be the finest orchestra in France at the time.
Split into simpler sentences: He worked at the Opéra and the Opéra-Comique in Paris before founding his own orchestra, the "Orchestre des Concerts Straram", in 1925. This ensemble was considered by some to be the finest orchestra in France at the time.