Concert Flute and Alto Flute Duet. This is an arrangement of Mozarts duo for flute and viola KV 423 for flute and alto flute. An extensive piece in three movements (fast, slow and then fast again), this piece was designed to give the alto flute some of the classical chamber music that is missing from the instrument's repertoire. Both parts are intricate and interesting; the two outer movements will require neatness of fingers and tongue, while the slow middle movement demands a singing tone and light playing from both parts. Flute 1 extends well into the third octave, and the alto flute part goes up to top E in the 2nd octave.