Overly academic performances have given the authenticity movement in music a bad name. No matter how scholarly the research, unmusical notes -- as one British musicologist neatly put it -- cannot possibly be correct notes. But when sensitive musicians put their hands on authentic instruments, the results, as Malcolm Bilson and Sergiu Luca demonstrated Sunday afternoon at the Library of Congress, can be both a joy and a revelation.

Bilson and Luca were continuing the series that features Mozart's sonatas for fortepiano and violin. These programs are historic in a double sense. They literally recreate the sound of Mozart's time, with Bilson using his own replica of a late 18th-century fortepiano and Luca playing a mid-18th-century violin with original fittings. The concerts also promise to alter permanently our conception of the proper Mozart sound, and even Mozart's ideas.

Curiously, the less powerful instruments (as opposed to modern grands and violins) make us more aware of Mozart's inventiveness. We hear much more, and what we hear has a fresh urgency, thanks to the unfailing musicality of Bilson and Luca's approach. Combining sure knowledge with strong feeling -- the approach of the best performers in any century -- they create an expanded expressive range within the more intimate sound scale.

The series continues Friday at 8 p.m. and Sunday at 3 p.m. It is a must for lovers of Mozart and music.