Sound-related noise names

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This page is in a collection about both human and automatic dealings with audio, video, and images, including


Audio physics and physiology

Digital sound and processing


Image

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Stray signals and noise


For more, see Category:Audio, video, images


Generating different types of noise can be useful for certain purposes, and names (often the colors) are often mentioned in such applications.


When measuring the amount of physical noise a device produced, you would often do so in an isolated room to reduce environmental noise.

Preferably an anechoic chamber so that you may primarily measure generated noise, not the reflected-and-filtered copies of the same, which would be measuring source and measurement environment.



Babble noise

Babble noise is a term regularly seen in speech-related auditory science, and often describes a recording in a place with many chatty people (e.g. an office or restaurant), (or an averaged spectrum of such).


Noise colors and other descriptions

Noise colors are often used when describing noise of different variations. Note that not all of these necessarily describe sound.


See also:

...and various others


Well settled noise colors

These three are more consistently defined than most others, sometimes in reference documents.

White noise

White noise is that in which the spectrum is flat: the pressure level for each frequency is the same.


Brown(ian) noise

Brownian noise, a.k.a. brown noise, is named for being produced by Brownian motion.

Its amplitude at a frequency is proportional to 1/f2. In other words, it falls about 6dB per octave, and has a dampened, soft, bassy quality.

Pink noise

pink noise is also called 1/f noise (see flicker noise below).

So its falloff lies between white and red/brown/Brownian noise.

Pink noise occurs both in nature and in electronic systems (where you should also look at the narrower term flicker noise, of which not all origins are well explained yet).

Pink noise is usually generated by filtering white noise.


Note that you could say that

white noise is 1/f0 (=1/1, i.e. constant)
pink is 1/f1 noise, and
brown noise is 1/f2,

...to point out their relations a bit more mathematically.

Moderately settled noise colors

Blue noise

Blue noise (also azure noise, and sometimes, ambiguously, violet noise(verify))

Blue noise has a power density that increases 3dB per octave (density proportional to f)

Also used to refer to other noise/distributions with minimal low frequencies.


Violet/purple noise

Violet noise has a power density that increases 6dB per octave (density proportional to f2)


Grey noise

Grey noise is often meant to be (white) noise subjected to an equal loudness filter. (e.g. A-weight).

Could be thought of a human-perceptual white noise.

Not-so-well-defined, sometimes ambiguous noise colors

These are less official in that they are not exactly defined, and/or are defined differently by different sources.

Roughly from best to worst defined, they include:


Red noise

Usually refers to Brownian noise.

Some authors seem to use it to refer to pink noise, though.


Black noise

Black noise is seen referring to multiple things, usually one of:

  • silence
  • a few spikes in silence, as e.g. in faxes (see also impulse noise, noisy white/black)
  • noise outside human-audible frequencies
  • noise with faster falloff than red noise: 1/fx noise for x≥3


Noisy white, noisy black

Mostly seen in the context of analog transfer of images.

Refers to an image area that should be white, respectively black, but has enough noise to visibly not be so.


Orange noise

Orange noise

  • often described as something like "a quasi-stationary noise with a finite power spectrum with a finite number of small bands of zero energy dispersed throughout a continuous spectrum."
  • the zero-energy bands coincide with notes in a scale/system of choice/interest, It leaves out-of-tune frequencies, which makes this less-than-pleasing noise.
  • reason for name seems to be association with sour, citrus; orange
  • "Orange noise is most easily generated by a roomful of primary school students equipped with plastic soprano recorders." :)


Green noise

Green noise

  • not very official at all, (according to wikipedia) usually one of:
    • long-term spectrum average of outdoor sites (similar to pink, with a 500Hz hump)
    • bounded brownian noise (how?(verify))
    • The mid-frequency part of white noise, used in halftone dithering [1]
    • voice-related noise, for testing telephone channels (verify)


See also