The small string ensemble that first performed chamber music to postwar European migrants in 1945 is now the largest presenter of chamber music in the world. The third biennial Musica Viva Festival is showing similar signs of growth and depth. In four short days from April 4 -7, the festival will present seven concerts and 30 other recitals, masterclasses, seminars, workshops, tours and talks at the Sydney Conservatorium of Music.