Southern Appalachia is known for its traditional homegrown music and for its fierce independence and cultural insularity.But when the majestic music of Beethoven, Brahms and Tchaikovsky soars up from a tiny point on the Cumberland Plateau — played by young people collected from 39 states and five foreign countries — that regional definition needs some revision. Now in its 49th season, the Sewanee Summer Music Festival (SSMF) at the University of the South is designed not only to educate but to inspire and expand the horizons of the 180 high school and college-age musicians who make up its talented but diverse student body during the five-week program. The Sunday afternoon symphony concerts at Guerry Hall offer evidence of the ability and determination of the students as well as the quality of the instruction that goes on during the week.From its modest beginnings, the SSMF built a reputation for quality and began to attract international attention under the leadership of Martha McCrory, a cellist based in Chattanooga.