Like most technically demanding styles, prog-metal is never any good unless you play it with conviction; add Floyd-like orchestral dynamics and Zep-ish mysticism, and you’ve got Sweden’s Opeth. Uruguayan bassist Martin Mendez has anchored the group since 1999, and he just keeps getting better. Blistering precision riffage is de rigueur (the head-banging “Slither,” for example), but Mendez gets to probe the outer edges of tone and color throughout the album; he uses a soft touch in the opening movement of the creepy ballad/anthem “Opeth,” and he’s a D-tuned heavy-treading golem in the epic “The Lines of My Hand.” Then there’s the jazz-fusion nugget “Nepenthe” and “Folklore,” where Mendez throws off fi nely wrought notes like an ever-branching and cascading river. Is this one for the true bass heads among us? Bet on it.