In keeping with the traditions of the Baroque and pre-Baroque eras, period-instrument orchestras consist almost entirely of strings, often augmented by harpsichord, double reeds, recorder, or timpani. They tend to number two dozen pieces or less, and the instruments–whether originals or replicas–don’t adhere to the tempered scale modern audiences are familiar with; to the uninitiated they often sound thin and out of tune. But the Toronto ensemble Tafelmusik can make a believer out of almost anyone. Its members bring conviction and authority to their performances, not to mention an intimate and irrepressible camaraderie that’s a joy to watch. Tafelmusik (literally “table music” in German) was founded in 1979, as the period-instrument movement spread to North America from Europe, and has been under the direction of violinist Jeanne Lamon since 1981. Over the years the group’s 19 core members have toured and recorded regularly, establishing a solid reputation for expressive playing, superb discipline, and a ready grasp of Baroque practices. (Old manuscripts are rarely annotated, so performers must understand what tempos, dynamics, bowing techniques, and even instrumentation would likely have been used.) Every performer is versed in the history of the 17th and early 18th centuries, both musical and social–though recently, perhaps in response to a trend in the period-music community, Tafelmusik has released CDs focusing on later composers like Haydn and Mozart. The group is traveling with 13 strings and a harpsichord; the featured soloist is Dutch recorder virtuoso Marion Verbruggen, renowned for her astounding expressive range and bold, fluid ornamentation. The program consists mostly of standbys from Tafelmusik’s core repertoire, including Bach’s Third Brandenburg Concerto and a concerto transcribed for recorder from BWV 1053; the fourth concerto from Vivaldi’s L’estro armonico, for four violins; Corelli’s Concerto Grosso in D; and Telemann’s Suite for Recorder and Strings in A Minor. Monday, 8 PM, Martin Theatre, Ravinia Festival, Green Bay and Lake Cook Rds., Highland Park; 847-266-5100. TED SHEN