You hear a musician use the words radical, experimental, avant-garde, and you think that the subject must be some young composer or newly minted piece that stretches, even threatens, our understanding of music’s boundaries. But it comes as something of a shock when the topic is, instead, music that’s a few centuries old.

Yet violinist Robert Mealy uses those words to describe the repertoire of the ensemble he codirects, Quicksilver, formed in 2009 to explore early Baroque chamber music. The ensemble made its local debut in an 11:30 p.m. slot at the 2011 Boston Early Music Festival. (“It was great — like a late-night jazz set,” Mealy said in a recent phone conversation.) They return on Saturday with a more conventionally scheduled show in the BEMF concert series.