Samuel Barber’s Violin Concerto, which dates from the 1940s (there were some revisions), is one of the great crowd-pleasers of the mid-20th century. Like much of Barber’s music, it’s sufficiently lyrical and accessible to please the more traditional-minded listener, while also being sturdy and strong-minded. And if you don’t care for the first two movements, the finale — which takes a sudden and somewhat mysterious swerve into extroverted display — is waiting in the wings with something different. The wonderfully thoughtful violinist Jennifer Koh is in the Bay Area on Sunday, Oct.