Pink noise: A spectrum of sound that is "correlated enough to create a pattern, but chaotic enough to be interesting." (Source: Gilden Lab, University of Texas.)
The New York Times's Natalie Angier recently reported on a new study published in the journal Psychological Science, "Attention and the Evolution of Hollywood Movies," about how the structure of films has changed to match the brain's natural rhythms:
According to the new report, the basic shot structure of the movies, the way film segments of different lengths are bundled together from scene to scene, act to act, has evolved over the years to resemble a rough but recognizably wave-like pattern called 1/f, or one over frequency — or the more Hollywood-friendly metaphor, pink noise. Pink noise is a characteristic signal profile seated somewhere between random and rigid, and for utterly mysterious reasons, our world is ablush with it.
Engineers and physicists classify noise according to its spectral density. The best-known classification, white noise, corresponds to white light, and has equal power in any band of a given bandwidth. Pink noise, by contrast, has equal power in bands that are proportionally wide. From the Wikipedia entry on the colors of noise:
This means that pink noise would have equal power in the frequency range from 40 to 60 Hz as in the band from 4000 to 6000 Hz. Since humans hear in such a proportional space, where a doubling of frequency is perceived the same regardless of actual frequency (40–60 Hz is heard as the same interval and distance as 4000–6000 Hz), every octave contains the same amount of energy and thus pink noise is often used as a reference signal in audio engineering. That is, the human auditory system perceives approximately equal magnitude on all frequencies. The power density, compared with white noise, decreases by 3 dB per octave (density proportional to 1/f ). For this reason, pink noise is often called "1/f noise".
In somewhat simpler terms, from Embedded Systems Programming:
Pink noise is evident in all forms of engineering and science from solid-state circuits to astrophysics and music. Unlike white noise, it bears a logarithmic characteristic, and, as such, represents a psychoacoustic equivalent of white noise sweetened for human ears. This is the signal used to test speakers and set equalization in theaters and other venues. When you tune up your home multimedia system, the noise used to drive the speakers for the volume settings is probably pink noise.
Noise comes in many colors other than pink and white, including brown, blue, violet, and gray.
You may be thinking that "Pink Noise" would make a good name for a rock band. You're absolutely right, and you're too late.