Cardiff's headphone pieces are recorded with two microphones placed on either side of a foam head. Unlike conventional recordings Cardiff's technique eerily reproduces sounds as they are heard from the inside of a human head. One of the things we are very good at as a species, as it turns out, is accurately judging the origins of sounds within three-dimensional spaces. If you hear a pencil drop behind you, you likely have a very good idea of exactly where to look to retrieve it. Cardiff's headphone tours take advantage of that, especially when played back in the same architectural spaces where they were recorded (her outdoor are not as effective). So walking down the staircases at PS1 accompanied by the headphone soundtrack commissioned for the museum, you hear the conventional sounds one expects to hear not just in a crowded museum, but in that exact crowded museum stairwell you are descending within. As a noisy group of middle-schoolers rushes up the stairs towards you from around a corner in the stairwell, you brace for their jostling bodies, only to have them pass around you - invisible phantoms existing only in Cardiff's recording. (Experiencing a Cardiff walking tour should be on any serious art lover's bucket list).
The Motet works almost the same way, but without headphones. The original recording was made with forty individual microphones arrange very much like the speakers, so if you place your ear against any one speaker you will hear an individual voice. But you will also hear sounds coming distinctly from corners of the room where there are no speakers.