- For similar phrases, see Brown note (disambiguation).
|Colors of noise|
In science, Brownian noise ( Sample (help·info)), also known as Brown noise or red noise, is the kind of signal noise produced by Brownian motion, hence its alternative name of random walk noise. The term "Brown noise" comes not from the color, but after Robert Brown, the discoverer of Brownian motion.
The graphic representation of the sound signal mimics a Brownian pattern. Its spectral density is inversely proportional to f², meaning it has more energy at lower frequencies, even more so than pink noise. It decreases in power by 6 dB per octave (20 dB per decade) and, when heard, has a "damped" or "soft" quality compared to white and pink noise. The sound is a low roar resembling a waterfall or heavy rainfall. See also purple noise, which is a 6 dB increase per octave.
Power spectrum 
from which we can conclude that the power spectrum of Brownian noise is
Brown noise can be produced by integrating white noise. That is, whereas (digital) white noise can be produced by randomly choosing each sample independently, Brown noise can be produced by adding a random offset to each sample to obtain the next one.
10 seconds of Brown noise
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- Gardiner, C. W. Handbook of stochastic methods. Berlin: Springer Verlag.
- Barnes, J.A. and Allan, D.W. (1966). "A statistical model of flicker noise". Proceedings of the IEEE 54 (2): 176– 178. and references therein
- "Integral of White noise". 2005.
- Bourke, Paul (October 1998). "Generating noise with different power spectra laws".
- Simply Noise, a free online white, pink, and brown noise generator that supports timer and volume oscillation functions.