It’s framed as a story of musical genius overcoming the odds: After the dissolution of his marriage and the “indefinite hiatus” of his platinum-selling band, Nickel Creek, mandolinist Chris Thile recruited several musician friends and then set out to fuse “formal music and folk music” by composing a so-called string quintet for bluegrass instruments. How to Grow a Band takes up with the group, christened the Punch Brothers, in 2008, as they face the difficulty of performing their four-movement, 40-minute breakup epic, The Blind Leaving the Blind. (At an early show in Glasgow, the band gets heckled by members of the audience who thought they’d paid for more straightforward bluegrass.) John Paul Jones and Yo-Yo Ma testify here to the rarity of someone of Thile’s stature trying to strike out in a new direction, and home-video footage shows the pint-size prodigy already plucking up a storm, but the film is most interested in the dynamics of the new band he has put together. Director Mark Meatto structures his film around The Blind Leaving the Blind so that each “movement” of the film also contains a significant portion of the corresponding part of the piece. There’s ample opportunity to admire the technical facility of the musicians and note their chemistry, and therefore appreciate their concern—expressed backstage and well out of earshot of their frontman—that Thile might one day find the project less creatively fulfilling than they do, and decide to move on. As it follows a group of seemingly well-adjusted professionals, How to Grow a Band might be a bit too low-key for the non-fan, but that’s not to say the tour doc lacks substance: It doubles nicely as a fly-on-the-wall case study in the demands of making music for a living.