Glaciers, permafrost, and the like are the kind of low-pass filter that lets people observe the underlying signal without a Matlab window open. For me, it's th

Glaciers, permafrost, and the like are the kind of low-pass filter that lets people observe the underlying signal without a Matlab window open. For me, it's the fact that the young children in my neighborhood have given up on hockey and now play pickup games of lacrosse on their driveways. See, older generations in Boston used to play on the ponds every winter. Today's kids cannot (ice thickness on the ponds is another low pass filter), and with only so much rink time to go around, they've largely switched sports. THey don't know the signal they're giving me, because they weren't around when hockey was the main game to play. But to me, they are the low-passed signal.