Highly informative and thoroughly endearing, this 1991 documentary by Rachel Liebling chronicles the “high, lonesome sound” and its legendary performers against the backdrop of a changing America. Created by Scotch-Irish settlers in the Appalachian Mountains, bluegrass gradually infiltrated the mass media, incorporating outside instruments (the mandolin) and styles (from syncopated African-American work songs to rock ‘n’ roll). The music’s journey is embodied by Bill Monroe, whose career began in the Kentucky hills in the late 1920s and ultimately took him around the world; among the other players on hand are Ralph Stanley, Earl Scruggs, and newcomers like Alison Krauss, none of whom minces words about the commercial compromises (electric instruments, the singing-cowboy phenomenon) and cultural forces (network TV, the Vietnam war) that have changed mountain music. Liebling’s sociological take is cogent and respectful, aided by vintage photos and newsreel clips, yet she lets the rollicking music speak for itself. 95 min. Gene Siskel Film Center, 164 N. State, Sunday, December 9, 6:00, and Thursday, December 13, 8:30, 312-846-2800.