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I've been interested in photographing helicopters lately. Partly because helicopters are just kinda nifty, and partly because there are a bunch of 'em that frequently fly nearby. So I've been keeping an ear toward hearing them approach so I can go grab a long lens and lean out the window.
When I'm experiencing fibromyalgia-related hyperacusis (auditory hyperacuity), I can hear them from too far away to be useful. Worse, I keep hearing sounds that resemble those made by helicopters, but aren't. I think that's from a certain pattern of truck traffic on I95. (Some nearer street vehicles also mimic helicopter sounds, but I can distinguish them more quickly because the direction the sound comes from changes in the wrong way. The sound that I think is coming from I95 has enough reflections -- the effect that makes 'ghosts' in analog television -- that it's hard to hear an exact direction in it. Reflections are a challenge regardless, but this seems to have extra bounces.)
I'm still trying to learn to distinguish street-legal motorcycles, scooters, and illegal dirt bikes by sound at a distance. The scooters and the dirt bikes sound awfully similar.