In 1984, a young composer and organist named Thomas Crawford founded his period band the Orchestra of the Old Fairfield Academy in Fairfield, Connecticut. In 2005, he rebranded as the American Classical Orchestra, resettling in New York, where the operation continues to flourish. Billed as a “salon concert,” an all-Bach program this month focuses on the composer’s “extraordinary capacity for musical consolation.” The opening selection, the motet Singet dem Herrn ein neues Lied (Sing unto the Lord a New Song) calls for a double choir, deploying eight voices in two four-part ensembles. A marvel of complexity, the culminating fugue represents the master’s supreme achievement in choral counterpoint—a fact not lost on Mozart, who was bowled over when he heard the score on a visit to Leipzig in 1789. No full score existed; to study Bach’s technique in depth, Mozart had to collate the individual parts and examine them side by side. Two of Bach’s best-loved motets (the introspective Ich habe genug and the jubilant Jauchzet Gott in allen Landen) round out the vocal portion of the concert. Then it’s the instrumentalists’ turn to take over. Their offering: the Orchestral Suite No. 2 in B minor—which is the key of the immense sacred compendium Bach called a mass, never mind that it’s incompatible with an actual liturgical service. —Matthew Gurewitsch