Although Elephant Revival comes from the bluegrass hub of Nederland—birthplace of the Yonder Mountain String Band—and employs a washboard from time to time, the band doesn’t consider itself a bluegrass outfit. Rather, according to its marketing info, the 10-year-old band is a “progressive transcendental folk quintet.” Loath as we are to agree with marketing material, the description seems to fit—especially after listening to the band’s latest LP, Petals (released April 1, Thirty Tigers). Few would say the previous Elephant Revival albums were particularly upbeat, but now the band just might have plugged into the sadcore genre. When paired with the eerie vocals of Bonnie Paine and Daniel Rodriguez, however, the vibe turns, well, hopeful. That’s especially the case on “Peace Tonight,” “Sea Monster,” and “Season Song,” in which Rodriguez rescues grim lyrics (“I saw death; that never dies”) by reaching for higher and higher notes. The result will provide listeners with a stirring sense of optimism—however fragile it may sound.