From the first notes of “Gospel Train,” as Melody Walker’s soaring voice entwines around the phrase “I woke up with heaven on my mind,” you’ll hear that Front Country isn’t your usual bluegrass band. When the fiddle and distorted acoustic guitar come crashing into the song like roaring waves, rushing back and forth with swelling ferocity, you’ll know that this is bluegrass unleashed, American roots music that refuses to be constrained.