Ever since its founding in 1979, the Toronto-based Tafelmusik has maintained a well-deserved reputation as the most invigorating yet graceful of period-instrument ensembles. Its members--most of whom are renowned Canadian baroque and early-classical specialists--play with intelligence and quiet authority, often achieving a beautifully balanced sonority uncommon for baroque orchestras. In violinist Jeanne Lamon Tafelmusik has a leader who's first among equals, an engaging pro who knows how to put together a program of entertainment informed by a strong sense of history. On a series of CDs on the Vivarte label, Tafelmusik champions authenticity with an utter lack of stuffiness: after all, the group is named after the baroque subgenre of after-dinner music. Another of Tafelmusik's virtues is its showcasing of minor masters: in addition to the obligatory works of Vivaldi (Concerto for Four Violins), Handel (Suite in G), and J.S. Bach (Concerto for Violin in A Minor), the bill of fare for this Ravinia recital includes the less familiar though equally delectable Suite in B-flat from Telemann's Tafelmusik and a Concerto for Two Oboes by the Venetian nobleman Tommaso Albinoni, a pioneer of the concerto grosso who's overdue for rediscovery. Monday, 8 PM, Martin Theatre, Ravinia Festival, Green Bay and Lake Cook Rds., Highland Park; 728-4642.