Air is sprayed in short bursts at 20 PSI through an Iwata Eclipse HP-CS airbrush connected to a 1/8 HP portable piston compressor. Because the compressor does not have its own air tank, the motor kicks in as the airbrush sprays to maintain consistent air pressure.
The sound of a small car driving by on W. Markham Avenue bordering Duke University around 2:00pm. I stood still and held my recorder, an iPhone 6, at my waist while standing on the sidewalk next to the street as the car drove past me.
From the adjacent sidewalk, I took this sound recording of an articulated bus passing through the tunnel leading to Duke's East campus. The audio begins as the bus approaches the entrance of the tunnel. The noise intensifies as the bus proceeds to halfway point of the tunnel where I stood holding the mic and then fades as it exits. Recorded on iPhone 5.