Bassist Trevor Dunn launched Trio Convulsant in 1998 with Debutantes & Centipedes, then shifted to the current personnel (guitarist Mary Halvorson, drummer Ches Smith) for the 2004 release Sister Phantom Owl Fish. On Séances, he expands the concept, adding the improvising chamber group Folie à Quatre, an intriguing, sonorous mix of strings (violist/violinist Carla Kihlstedt, cellist Mariel Roberts) and woodwinds (Oscar Noriega on clarinet and bass clarinet, Anna Webber on flute and alto flute). Dunn’s abiding and somewhat macabre fascination with the “convulsionnaires,” an extreme Christian sect in pre-revolutionary France, provides the jumping-off point for these intricate, intensely rhythmic compositions. Playing mainly pizzicato upright bass, he leads the group through complex grooves with dense passages of written counterpoint, in which each player displays not only great virtuosity, but also true musical character. After the broken-up funk of “Secours Meurtriers” and “Restore All Things,” the beboppish “Eschatology” comes as a surprise, its warped yet precise unison theme for bass and alto flute recurring in new instrumental pairings until the very end.