There was once a time when the Magnetic Fields could be mistaken for a rock band at their live shows. That was a while ago. Their two-set performance at Brooklyn Academy of Music on Saturday night was as sedate as any other evening of chamber music: they were seated with music stands in front of them, quietly playing (or not playing) acoustic instruments as each arrangement required. Songwriter and bandleader Stephin Merritt wore a knit cap and a dour expression, strummed a little ukulele, and bickered between songs with keyboardist/majordomo Claudia Gonson — their onstage relationship is affectionate camaraderie that expresses itself as poorly suppressed irritation. Gonson excitedly pointed out conceptual elements of their set list (apparently a lot of the Magnetic Fields' repertoire involves vampires); Merritt muttered laconic explanations of a few songs. (It turns out that the waltz-time lit-crit kiss-off "Always Already Gone" was initially meant to be an Ink Spots pastiche.)
The lineup was the quartet — Merritt, Gonson, cellist Sam Davol and guitarist John Woo — that's been the core of the Magnetic Fields for 15 years or so, augmented by their occasional collaborator Shirley Simms, who played an autoharp and sang some of Merritt's more countryish numbers ("I'm Sorry I Love You," "Kiss Me Like You Mean It"). Their current tour — which returns to New York for three Town Hall dates in March — is ostensibly to promote their new album, Realism, most of which got aired. Merritt's got an enormous bag of songs at this point, though, and the evening's most surprising moments came when he pulled out acoustic arrangements of long-lost charmers: the band's debut single "100,000 Fireflies," the 1991 obscurity "Falling in Love with the Wolfboy," a handful of songs first recorded by their long-inactive sister band the 6ths. And the R-rated, Simms-sung lament "The Nun's Litany," which had been drenched in torrents of feedback on 2008's "Distortion," turned out to be just as funny with the volume turned almost all the way down.