Amazon.com essential recordingMention Bach's Trio Sonatas to aficionados, and chances are they'll think you're talking about organ music. But Bach did compose four trio sonatas in the original sense of the term (the "trio" being two melody instruments with continuo), and they get excellent performances here by London Baroque. These works are in the four-movement, slow-fast-slow-fast form of the 17th-century church sonata; they combine some of the spontaneity and intensity found in Corelli's sonatas with Bach's unsurpassed skill in harmony and counterpoint. This recording was made in the mid-1980s, when London ruled the period-instrument world; 15 years later, the performance holds up well. The only noticeable flaw is in the Sonata in G Major for two flutes: the beautiful opening movement lies low in the instrument's range, and the flutists' phrasing and tuning sound tentative. (The players sound much more comfortable in the sonata's faster movements.) The two sonatas for violin and flute get beguiling performances--in particular, the sonata from the Musical Offering radiates charm and has no trace of the dour intellectualism that often afflicts performances of that masterpiece. London Baroque's rendition of the Sonata in C Major for two violins is even better, as lively as anything that youngsters like Il Giardino Armonico have come up with since. --Matthew Westphal