Brown noise is a type of noise similar to
white noise, but rather than having an
equal representation of all
frequencies, the lower frequencies are represented more than the higher ones. This
results in brown noise being much more
pleasant to the ear.
Natural sources of brown noise include
waves breaking on a shore,
wind blowing past your ear, and so on.
White noise may have equal representation across the spectrum, but due to the way the
ear perceives sound, the
high frequencies seem to be much
louder.
One
interesting thing about brown noise is that it's easier for you to
imagine sounds in your head when listening to it, because your ears are receiving
neutral stimuli and the
brain can pick up what it wants from the
palette.