It doesn't feel like four years since we've heard from Satyricon, does it? Aside from a live album with an orchestra, the biggest news relating to the band since 2013’s Satyricon was Sigurd 'Satyr' Wongraven's announcement of having been diagnosed with a brain tumour. Thankfully, it's benign, but the knowledge that invasive brain surgery will ultimately be required must have hung over Satyr during the making of Deep Calleth Upon Deep, and it's not difficult to feel that it’s just that little bit more intense and emotionally infused as a result. The change from Satyricon is huge, that unfocused, meandering rock abandoned altogether in favour of something like a more progressive take on the groovy blackened metal of The Age of Nero. It results in an album that feels like a natural successor to that, definitely more akin to what we've come to expect of Satyricon, albeit an album that takes its time to grow on you and nearly altogether lacking the hooks that we've come to expect.

Not that Satyr cares about our expectations, of course! No band sounds like Satyricon, their blend of black metal, groove, and atmospheric rock being quite unique. Yes, they're still remarkably close to black metal despite having left the genre's purity behind long ago; atmospherically dark and serious, no hint of a smile cracking the face. Black Wings and Withering Gloom especially is about as close to black metal as Satyricon have been in a long time, a blizzard of riffs and lyrics talking of 'snow-covered mountains up north' having terrific impact even as the track devolves into proggy groove in its centre. The title track isn’t far behind, near-operatic backing vocals from guest Håkon Kornstad initially seeming part of the backdrop but taking the fore as the instrumentation is allowed the helm, the song ultimately tied together with a bizarrely uncatchy chorus. Even opener Midnight Serpent isn't the sort of catchy banger that you'd think the band would open with, instead sticking mainly to a mid-paced groove before turning atmospheric and dark at the halfway point, longer than it seems at six minutes plus.

There are plenty of highlights, but often they take time to reveal themselves and none are flawless. Blood Cracks Open the Ground seems playful and straightforward initially, with repeated motifs and melodic trills, but soon reveals itself to be a more complex and technical beast, a blackened prog work-out that struggles to hold together cohesively due to its looseness. The saxophone-enhanced Dissonant works well, feeling like modern Ihsahn and almost like a blackened King Crimson, anchored with Satyr's snarled vocals and a typically flamboyant drum performance from Frost. Strangely, Satyricon's limited experimentation with jazz here feels utterly natural and is far more compelling than other tracks; it could and definitely should have been taken further. Conversely, To Your Brethren In the Dark is disappointingly old-fashioned, a slow, dark hymn that goes on a little too long and holds no surprises yet is solid enough.

Finale Burial Rite will probably seize most listeners' attention, adding subtle textural variety with clarinet, bassoon and French horn in the background. It's perhaps a little too limited an addition to be truly remarkable, complimenting the metal elements rather than rivalling them in line with past experiments, yet given what a deliberately limited palette Satyricon often paint with this and the saxophone of before are more than welcome touches. Many modern-day albums from the band are notable for their tight control; the fixed tempos of Now, Diabolical, for example, saw Satyr and Frost striving against their own constraints, and it sometimes feels like they've barely broken free from the near-smothering groove introduced on 2009’s Volcano. Yet we've seen the band strike out into new terrain multiple times before, and although Satyricon was by and large something of a failure (even as it gave us one of the band's more beautiful songs in Phoenix), the memory of diverse victories like Nemesis Divina and Rebel Extravaganza show the genius that made Satyricon's name. Hopefully the start of a new era, then, Deep Calleth Upon Deep is an interesting if imperfect step onward, and it will be genuinely fascinating to see what the band do next.