It’s easy enough to measure the health of bluegrass by looking at the music’s upper crust, but what about below the surface? From a musical — if not an economic — point of view, things are looking pretty good when you turn to groups like the Tina Adair Band. Ms. Adair herself is a fine singer who popped out one dandy project for Sugar Hill back in the ’90s, and her husband, Tim Dishman (formerly with Special Consensus), is equally convincing in that role. Banjo man Sim Daley is still better known as a master luthier, but his picking is sure and steady, while bassist-about-town Forrest Goodman holds down the low end. Don’t expect boundary-busting innovation, but that’s kind of the point — the Tina Adair Band keep it between the lines, but nevertheless make bluegrass that’s tasteful, creative, engaging and more than satisfying enough to make an evening with them worth your while.