I love all of your variations, thank you so much for this! I combined them into this one, which I really like, but I think I will play around a bit more :)
That 2nd link in 'b'rown mode immediately makes me feel like I'm standing on the seashore on an overcast day... for some reason it brings memories of Disco Elysium. Exactly what I need today, thanks.
To me, these sounds produce fatigue. When I used to travel frequently by air, I had a habit of wearing noise-cancelling headphones just to try to suppress the background, whether or not I actually played any other media over it. I didn't really like the leftover hiss, but cutting the deeper sounds seemed to reduce my fatigue anyway.
So, I am wondering how brown noise fans find the noises of travel. The different synthesizers posted in this thread overlap a lot with highway and airliner environments for me. Different vehicles had different equalization, of course.
Another sound this reminds me of is the old background rumble they put in the Star Trek Next Generation TV show to represent their shipboard environments.
Despite the sliders being a straight line, it's not really brown noise, as the slope starts going down again below 550Hz. (Which is a good thing in terms of being nice to listen to: this sounds more natural, and pure brown noise has too much bass to use with headphones.)
I was able to get pretty close (80% ?) in Audacity with Generate > Noise > Brownian Noise,
followed by Effect > High-Pass Filter > 550Hz (12dB roll-off).
If you come up with anything please let us know.
[1] https://www.cloudacm.com/?p=3145
[2] https://mynoise.net/NoiseMachines/whiteNoiseGenerator.php