Laws of Gravity (Compass, 2017)

The Infamous Stringdusters have always been difficult to categorize. That's part of their charm. Part traditional bluegrass (leaning on sound bluegrass instrumentation, namely guitar, Dobro, banjo, fiddle and standup bass), part jam band (extended sets of songs in their live shows in which one song triggers another), and wholly original with a signature sound and energy that goes on without cease.

In the last year, The Infamous Stringdusters have released an album of duets with female singers (" Ladies and Gentlemen") to great effect, released an EP of covers and found their names creeping ever-higher on the posters of some of the biggest music festivals in the country.

"Laws of Gravity" drives their momentum forward. The songs are well-crafted, admirably played and display assuredness.

The Infamous Stringdusters' whole is demonstrably greater than the sum of its parts; it's what a musical collaboration can achieve if talented players emphasize their strengths and manage their weaknesses. The songwriting is true to the traditional music form, but never seems cut from a pattern. The singing is good, but doesn't overshadow the individual playing, which is the essence of The Infamous Stringdusters. "Black Elk," for example, features a tasty lead vocal from Andy Hall, but makes its mark with a startling interplay of guitar (Andy Falco) and banjo (Chris Pandolfi). Bassist Travis Book sings " Back Home" with back country soul that calls to mind the "Sittin' In" masterwork of Jim Messina and (pre-pop) Kenny Loggins. (That is intended as high praise, for the uninitiated).

The instrumental work is crisp, bright and layered. Hall's Dobro lines never disappoint, and Falco is as hot-blooded an acoustic guitarist as you are likely to encounter these days. Garrett's fiddle is inspired, sometimes breakneck and never mild. Pandolfi and Book, banjoist and bassist, respectively, are the percussive bedrock of the band. The Stringdusters go nowhere without them driving the train.

Strictly speaking, there is only one instrumental number. "Sirens" has appeared here and there in the band's stage show since early 2016, and it is present in "Laws of Gravity" as a barely-contained musical roundabout in which each member of the band gets a chance to strut his stuff in a familiar AA/BB pattern. Falco starts out, Hall rolls in and then (anchored by Book's bass line), Garrett's fiddle and Pandolfi's banjo exchange figures before the whole thing comes crashing back around. It's great fun.

"Laws of Gravity" is a satisfying work by a crazy-good band, rich with confidence and purpose.