As various features of genuinely progressive ‘70s rock have calcified into a flashy, often color-by-numbers genre known as “prog,” it’s been under-acknowledged that the true vitality of that earlier era has flourished in the underground. Case in point: the brilliant second album from Pittsburgh instrumental adventurers Don Caballero. Hearing a track like “Repeat Defender” which brilliantly juggles riffs, dynamics and time signatures across 11 enthralling minutes while maintaining a strong narrative throughline, one feels compelled to clear space on every King Crimson, Yes and Magma fan’s shelf for the entire Don Cab catalog, but particularly 2. This was the effort where they leveled up masterfully from For Respect, their blunt yet brainy 1993 debut, and learned how to sustain compositional intrigue across lengthy forms. It’s also the album where Damon Che emerged as perhaps the single most impressive rock drummer of his generation, a tornado of virtuosity and edgy invention whose flailing runs across Rototoms and ride-cymbal bell on tracks here like “P,P,P,antless” rival peak Bill Bruford or Neil Peart for sheer mind-boggling incandescence. Elsewhere, the band — also including guitarists Mike Banfield and Ian Williams and bassist Matt Jencik, also of Hurl — sounds just as comfortable with airy mood-setting as with ferocious math-metal riffage. Forget unhelpful classifications and myopic scenes: This is the true spirit of modern prog.