There are drones, and they are varied, and amid those drones are drones that are something else in disguise. Sometimes that something else is a trick of the ear, a figment surfacing in the sonic Rorschach test of extended abstraction. Sometimes it’s something buried just below the surface. If ambient music inherently explores the liminal, presenting a still surface that suggests untold action underneath, then a track like Szymon Kaliski’s superb “2018-12-13” plays with the ear by introducing elements hinting at a more formal music that never comes into focus. The piece opens with a dense drone, like the start of Simon and Garfunkel’s “El Condor Pasa” but pitched down an octave and left to loop seamlessly. The saddest sound, indeed, it progresses by not progressing, by instead gathering its hidden depths only so much that a glimpse of what might be a piano or an orchestra appears underneath. That such extremes might be confused for each other is a clue to the intensity of Kaliski’s stillness.