I was lying in bed with my son the other night, having some quiet time after the completion of his bedtime story. I insisted on the light being out, which he didn't mind too much with me there. As we snuggled up, I head a train clacking and blowing in the distance. The train tracks in question are about two miles from our house, were you to measure out a straight line. That's a pretty good distance over which to get clear sounds, but there's a lot of open land between us and the tracks. We live fairly close to an airport (the sky is rarely empty over our house), but get relatively little noise from it. I talked to my boy for a minute about the noises, but he wasn't paying a lot of attention; it was dark, and he was tired. The thoughts persisted for me, though, and I got to thinking about other night sounds I've known.
I grew up fairly close to a "main" road (as things go in West Virginia), and less than a quarter mile from an Interstate. I learned to sleep to car sounds and the rumble of tractor trailers on an overpass. It seemed comforting that no matter how late my insomnia kept me up, there was always someone out there in the same boat, running around in the night. I could hear the cars for some distance as they approached, the sound rising and falling. That wasn't all when it came to night sounds, though. Living in an ancient trailer (and trailer park), there were always creaks, sounds of movement, people talking. Things were never quite quiet, and anything out-of-the ordinary would wake me up fast. One of the more important sounds, though, was one I almost always slept through.
Dad was a volunteer firefighter, so he carried a pager for station calls. I still remember the pattern that distinguished calls for his station from others on the frequency -- a long low tone, a long high tone, and then about ten or fifteen fast, pulsing tones. And, as it was supposed to be an attention-getter, it was loud. I mean, "the neighbors across the road heard it" loud. Being for a volunteer emergency response group, there were no shifts, and things happen at all hours. However, no matter how many times my father (and later, brother) left the house to fight fires in the dark of night, I almost never woke to the pager. Occasionally, I'd hear them running through the house, or a door slam, but never the two or three pager calls. My rare bouts of sleep had tuned them out; somewhere in my brain, something managed to say "not for you". That's something that's both served me well and harmed me over the years.
My brain is good at sorting night sounds into "no problem" and "weird, needs action". That it can do it at all is one of the few things that allows me to sleep, the fact I still wake up at night has a tendency to make me a bit paranoid when it happens. Even in college, the smallest sounds would filter through. My first dormitory has an issue with people pulling the fire alarm at night. Sometimes it was random, sometimes it was on a schedule. What most people didn't notice was that the alarm was wired in such a way that you could hear an electric hum traveling through the system before the siren actually went off. My brain learned to wake up during that second and a half of hum, so that I wouldn't be startled awake by the alarm. Often, I'd be swinging out of bed before the alarm sounded. I also had a far more accurate internal clock while asleep than awake. When people were pulling alarms on schedule, or when I consistently woke with an alarm clock, I'd almost always wake a minute or so before they sounded, because I didn't like waking to noise.
The same thing happens with my family. I can sleep through most anything, but I've woken to my kids' breathing patterns changing on the other end of the house. That was as a new parent, though. My brain has learned when to take notice. I think, ultimately, I end up missing some things I'd like to hear, though. I like nighttime. I like hearing insects and animals, and we live in a rural enough spot to get some of that. I like hearing that train in the distance, no matter when it comes through. I guess I'll just have to close my eyes and listen more.