Some of our favorite Christmas melodies are dressed-up versions of Renaissance carols and songs. When the London-based Renaissance choir group, the Tallis Scholars, joins Washington's Folger Consort to perform a series of special holiday concerts this week, these melodies will be performed as they were 300 years ago.

"We're doing them in the original way, not with any recent harmonization or dressings up that happen to these melodies. They're pure," says Peter Phillips, director of the Tallis Scholars. Among the better known melodies to be performed are "Lo, How a Rose E'er Blooming," "Greensleeves" and "Nowell Sing We."

Phillips founded the group in 1978 while studying organ and Renaissance music at Oxford. The ensemble takes its name from Thomas Tallis, a 16th-century English church music composer. The group's last U.S. appearance was at a 1982 concert in honor of Shakespeare's birthday at the Folger Library.

"It's an exciting experiment for us to appear with an instrumental consort," says Phillips, explaining that the eight-member group usually performs unaccompanied. "When we rehearse by ourselves, we concentrate on blend -- getting all these eight singers to make a homogenous sound. Incorporating instruments into that is a new challenge -- it gives extra color, which is tremendously important."

The concerts, all at the Folger Library, will be held today at 3 and 7 p.m., tomorrow at 8 p.m., and Friday and Saturday at 8:15 p.m. There will also be a matinee at 3 next Saturday.