Darkest Hour’s music is a hybrid of two severe subcultures – merging hardcore punk riffage with the shrieked vocals and blast beats commandeered from Swedish black metal. The tunes are complex, almost to the point of abstraction. Glassy harmonies zigzag into brutalist pounding. Darkest Hour has never mellowed out, but is has become increasingly tuneful over the years. On the group’s most recent record, “The Human Romance,” vocalist John Henry tweaks his growl-to-melody ratio in the latter category’s favor, grumbling fully sing-along hooks. And the band’s arrangements have become less claustrophobic, frequently indulging in spacious interludes.