With all the predictable and sometimes crass hubbub associated with Christmas, it's consoling to know that the Folger Consort's quiet manner of holiday celebration is once again available for those who prize musicmaking with genuine old-fashioned values. The group's medieval Christmas program, which began a six-day run Tuesday night at the Shakespeare Library, encompasses 600 years' worth of material drawn from French, Italian and English sources. Some of it is merely quaint, but the Consort plays with such vitality that one appreciates even those pieces having marginal relevance to the season. This six-centuries-of-Christmas scheme has pipers piping, fiddlers fiddling, pluckers plucking and one golden voice belonging to guest soprano Johana Arnold.

The pace never flagged and the instrumentation changed regularly, beginning with 11th-century songs whose modal melodies often used drone accompaniment. In "Noster cetus psallat letus" ("Let our congregation sing") Arnold's voice was doubled by Scott Reiss's recorder, a simple device that added poignancy to her lines. Supporting Arnold by himself, Christopher Kendall on harp created a stark yet meaningful setting for the 15th-century English carol, "There Is No Rose."

Kendall (on lute), Reiss and multi-fiddler Robert Eisenstein got stronger as the music got newer. They provided an attractive framework for "While Shepherds Watched Their Flocks by Night" and, led by Eisenstein, performed a neatly embellished instrumental arrangement of "Greensleeves." For an encore, the Consort abandoned its historical game plan and usual decorum by tackling "White Christmas." Reiss interjected snippets of "Jingle Bells" and "Deck the Halls" in a sendup suggesting the group had taken one too many nips from the wassail bowl.