You may have heard of the term “white noise“, and seen “white noise generators” marketed as sleeping or concentration aids, without knowing exactly what white noise was. Colloquially, “white noise” may be thought of as random noise which is evenly spread over the entire frequency spectrum (Pure white noise is an idealization, but it can be approximated over a given frequency range. I won’t get into randomness here). Clearly, the term “white noise” takes its cue from “white light”, which is the sum of all colors of light before they are refracted through a prism.
In keeping with this theme, there are other “colors” of noise. There is “pink” noise, which is random noise which attenuates (or weakens) at the rate of 3 decibels per octave (i.e. it halves in power for every doubling of frequency). “Red” noise drops off at 6dB per octave. Red noise is sometimes called “Brown noise”, but Brown in this case refers to Robert Brown of Brownian motion fame, and not the color!
Going the other direction, blue noise and purple noise increase at 3dB and 6dB per octave, respectively. Each color of noise has a distinctive sound and it’s interesting to compare them. White noise generators are sometimes used to “jam” distracting ambient sounds or simply to provide relaxation. I prefer Brown noise.
Now for something useful. Linux comes with a very handy audio utility called sox which includes the ability to generate noise. I got the idea from this blog when looking for WNG software. The frontend to sox is the play command.
Here’s an example:
play -n synth brownnoise
pinknoise and whitenoise options are also available.
sox is useful for many more purposes than generating noise, so it’s definitely a utility worth looking into. For those who prefer to get their noise at retail, there’s SimplyNoise.