Bach: Cello Suite No. 6 in D Major, BWV 1012 (September 17, 2006)Bach: Air on the G String, BMV 1068 (arranged for flute solo)(December 10, 2006)One of the interesting things about Bach, many singers will tell you, is that he likes to use voices like instruments. On the flip side, Bach also sometimes liked to write for instruments in ways that made them sound like voices, as in this week’s episode. In Bach’s suite, the cellist plays the roles of “soloist” and “orchestra” simultaneously, playing both the long, singing melodic lines and the underlying harmonies. Next on the program is one of Bach’s most famous melodies, in an arrangement for flute solo, played by flutist Paula Robison. The title “Air on a G string” actually wasn’t applied to the piece until much later, when a 19th-century violinist transposed Bach’s work down a whole step so that he could play the entire melody on the G string of his violin, the instrument’s lowest string, giving it the lush, romantic era sonority many of us have come to identify with the piece.