Offret is the duo John Spell and Matthew Swiezynski, and “Ester et Iselin” is their nearly 13 minutes of reckoning with mechanical drones. It’s a track of deep tonal loveliness that masks an underlying industrial intent. Beneath the hovering warmth of a dark, low-register moan is an extensive array of factory noise: machine tools, overworked engines, metal shards, acetylene torches. Of course, none of that is actual source audio, necessarily, just associative comparisons of the sounds. The track is a live recording, posted by the Invisible Birds label, made on September 16, 2015.