Swiss thrashers Coroner’s fourth album, 1991’s Mental Vortex, is commonly regarded as their masterpiece. And it is a great record, but new listeners should approach with expectations tempered. The sound is extraordinarily dry, comparable to Prong’s Beg To Differ or Metallica’s …And Justice For All. Thomas Vetterli’s guitars are like a table saw cutting through sheet metal, harsh and unremitting, but then he’ll overdub a gentle acoustic to shadow the distorted main riff. Ronald Broder’s bass is minimally present, often more of a low rumble deep in the mix than a second instrumental voice. Markus Edelmann’s drumming is pinpoint precise, with almost none of the whomp of metal; he could be playing a four-piece jazz kit. The songs twist and turn, leaping sideways without warning, speeding up and slowing down and rarely hewing to a simple 4/4 rhythm; there’s a lot of syncopation and even a weird kind of swing to Edelmann’s playing. Samples of movie dialogue, news broadcasts about the assassination of US President John F. Kennedy (on “Semtex Revolution”) and a few eerie sound effects demonstrate an awareness of the larger world, but Mental Vortex is often a very claustrophobic album, trapping you in a small space with three men focused on their work. And then it all ends with a seven-minute cover of the Beatles’ “I Want You (She’s So Heavy)” that both works and doesn’t. They Coroner-ize the song pretty well, but they also wind up sounding more like a “normal” metal band in the process, with Broder’s bass moving to the fore and the guitars going all hard rock.