The double bill at Wolf Trap last night was an odd one. The Kronos Quartet, those radical experimenters of classical music, played a set followed by the Modern Jazz Quartet, those genteel conservationists of jazz, and the two chamber groups joined forces for a final set. The fact that they meshed so well says something about the relative positions they represent, but it also says something about their shared commitment to precise concert arrangements of repertoire rarely given such treatment.

In the final set, the combined octet played four works for jazz quartet with string quartet composed by MJQ pianist John Lewis. Harmonic construction has always been Lewis's forte, and the sustaining strings filled out the gently swinging pieces most fruitfully. Moreover, Kronos provided a rhythmic tension often lacking in the laid-back MJQ arrangements. Lewis had a light, graceful touch at the keyboard, and his band mates played with a similar sense of restraint. In their own set, the MJQ played two Ellington pieces (plus Lewis's "For Ellington") with a softness that captured his harmonic subtly at the expense of his emphatic drive.

As it often does, Kronos capped its set with Jimi Hendrix's "Purple Haze," but last night paired it with a newer, similar piece, Steve Mackey's arrangement of Bo Diddley's "Road Runner." The two violins played the high vocal phrases, while the viola and cello rocked to the Diddley beat. John Zorn's "The Dead Man" proved overly gimmicky, but the evening's highlight was "Jabiru Dreaming," which Australia's Peter Schulthorpe wrote for Kronos this year. The lulling phrases seemed to slip and slide in and out of harmony; melancholy solos were played against plucked and tapped rhythms, and the violins smoothly incorporated bird and insect sounds into the enchanting music.