Brown noise is noise whose energy falls away as pitch rises, so almost everything you hear sits at the bottom of the range, a deep rumble rather than a hiss. On greensound it is built by adding a small random step to the last sample, leaking the total back toward zero, so it never drifts off to one side.
Why is it called brown?
Not for the color. It's named for Brownian motion, the random jiggling of particles described by the botanist Robert Brown, which the way it is built resembles.
Brown noise or white noise?
White noise, on greensound, sounds even and hissy across the whole range you can hear, with nothing weighted more than anything else. Brown noise sounds like a low, steady rumble, with very little left at the top of the range. Set next to each other, white is the brighter, thinner one, and brown is the heavier, darker one.
Brown noise or pink noise?
Pink noise sits between white and brown in how steeply its energy falls off with pitch, roughly 3 dB per octave against brown's roughly 6. It is made differently too: pink runs white noise through a filter of six parts added together, where brown is a single running sum.
How is it made here?
Each new sample starts from a fresh random value, scaled down to a small step, and added to the previous output; that running total is then divided down slightly so it leaks back toward the middle rather than drifting to one side over the length of a session. Its energy stays roughly flat below about 150 Hz and falls off at roughly 6 dB per octave above that, rather than dropping evenly across the whole range. That's the entire process — no recording, no sample library and no loop sit behind it, and it's generated fresh in your browser every time you press play.