The human brain is amazing, and more sophisticated and complex than the most powerful computers being built today. You don’t think about your brain all day. It’s just there and it (hopefully) does what it’s supposed to do.
The brains of some seasoned radio amateurs and short wave listeners appear to have developed in such a way, that they mimic a modern DSP unit. Interference, noise, carrier tones and other annoying sounds are filtered out with relative ease. All that remains is the signal they want to hear.
I didn’t realize that until I got some (iPod generation) visitors who wanted to see my shack. I switched on some classic rigs and let them listen to all those short wave signals. Band conditions weren’t optimal at the time, but good enough. At least, I thought they were.
As usual, I made some notes about the stations I heard, such as call signs, personal names and the rigs they used. To my surprise, my visitors couldn’t figure out any of it – they just were not able to isolate the voices from the interference. All they heard was background noise, static and wisthling sounds.
Amazing, these Ham brains of ours.