I found myself having to explain what a crowd meant to me. A friend is inviting me to his Halloween party and I want to go if I finish my costume. However, if I am having an overstim-rific day, I'll have to decline.
He explained that there would only be about ten people, including me. That is when I realized that my view of "crowd" and his didn't match. Every person I am near has a smell, a voice, and actions. That is a lot of input! I do best in crowds of four. Or fewer. Fewer is best. Two is nice.
I don't think that NTs are very aware of their senses unless something is overwhelming. They don't recognize everyone's scent, but are certainly aware if someone has a very strong scent. They are aware that everyone has a voice, but they are able to block out the ones they aren't actively listening to.
Filters are something almost entirely lacking in autistics. Being able to block out one sense, or part of one sense, is something akin to magic to me. I cannot imagine how it works or how it would feel to do it. What do you see and hear if you are randomly blocking stuff? How does it work? Don't you miss out on things?
It's a great mystery to me. Probably as much a mystery as how I manage without any filters is to NTs. They would need the inverse of a sensory deprivation tank to understand it!