The Infamous Stringdusters have never had anything to prove as forward-thinking instrumentalists, but over time the quintet’s songwriters have become more daring too, perhaps taking a cue from the Steep Canyon Rangers in exploring existential issues. Let It Go represents a full flowering of the band members’ considerable gifts in its authoritative picking and fiddling, in the vocalists’ earnestness, in the well-crafted songs’ themes. Andy Hall’s “Winds of Change” illustrates all of these attributes: its narrative begins in an intense moment of self-doubt but evolves to counsel fearless self-reliance in the face of the unknown. Meanwhile, the fast and furious dialogue between dobroist Hall and redoubtable banjo man Chris Pandolfi mirrors the singer’s internal storm. The same urgency informs a Jeremy Garrett co-write with Jon Weisberger, “Where the Rivers Run Cold,” a soaring, banjo-and-dobro-fired communiqué centered on the singer’s refusal to let personal misfortune keep him from leading a fruitful life. In the end, on the title track, the a cappella southern gospel blend of voices says it all, singing “if you think you can make a difference…let it go.” The Stringdusters’ production—big, bright with a sonic edge like a rock album—assures the messages getting through unfiltered.