Fans of pianist Angela Hewitt will be delighted to hear her in a chamber music setting, accompanying Andrea Oliva (who was described as ''one of the best flutists of his generation'' by Sir James Galway) in a program of J.S. Bach's Sonatas for Flute. Of unfailingly remarkable quality, all these works exploit the full potential of an instrument which was only just coming into its own when they were written. Oliva's lyricism and agility coupled with Hewitt's musicianship - not to mention her lifelong rapport with Bach's music - make this an album to treasure.