Are ORB heavy without the metal? Or are they metal without the heavy? Explaining the Australian band's formula is a good bit harder than simply enjoying it.

On their second album, 2017's Naturality, ORB hit a bit less hard than they did on their 2016 debut Birth, and a dash of prog rock seems to have found its way into their sound on numbers like "You Are Right" and "Rainbow's End." But for the most part, ORB aren't changing up their attack so much as they're evolving, and the key ingredients are still the same.

Guitarist Zak Olsen still worships at the altar of Tony Iommi, with Leigh Stephens as a patron saint, working out tangled, buzzy guitar riffs that harken back to the first era of heavy rock, though they seem a dash more artful than they did on Birth.

Bassist Daff Gravolin lays down a solid bottom end that gives Olsen sure footing for his explorations of the musical space around him, and drummer Jamie Harmer brings color and texture to the performances as well as keeping the beat and pushing the songs forward.

The production on Naturality is just a bit more refined than before, and the use of period reverb on Olsen's voice is a nice touch, though for the most part the recording and mix are admirably straightforward and uncluttered.

And while it's not hard to spot the influences in play here, ORB are good enough that they don't sound like they're lifting tunes from other bands, but have learned how to write in that tradition without turning to plagiarism.

Given how devoted ORB are to sounds of the past, it may have been hard to imagine them growing as a band, but they've subtly done just that on Naturality, and stoners and doom aficionados alike will dig this.