There was a festival atmosphere in Liberty Hall on Wednesday night and not just because the crowd was large and loud (though that helped). There was also that ineffable flow and unspoken dialogue among the four bands, softly conveying the spirit of roots music in all its complimentary forms. The timeless but mysteriously innovative folk/gospel flavor of Birds of Chicago gave way to the pure mountain-tinged songwriting of Jill Andrews. The bluegrass second half paired young and hungry Billy Strings with one of his heroes, the sixtysomething but unaware of it Jerry Douglas. His band came with a jazz/grass/rock fusion mode that tickled my every musical nerve ending. Keep on the grass? Good luck with that.