16. White noise, pink noise...orange noise?
This page is mostly for fun, so
don't take it too seriously!
You've certainly heard of 'white
noise', which is calqued into
Chinese as ¥Õ¦â¾¸µ bai2se4 zao4yin1. It is not hard to
understand why this term was chosen. White noise contains an
equal distribution of energy spread over all frequencies, just
as white light is composed of all of the colors of the spectrum
of visible light; here is a
more detailed explanation. Click here for an
audio sample.
You hear white noise when no
signal is being broadcast over a television channel or radio
station. It's not just an annoying, unpleasant sound ¡V some
people use it to sleep better, e.g. by running a fan during the
night. This works because steady sound at all frequencies can
mask all kinds of other noises that might disturb a light
sleeper. There are even commercial products
that emit white noise to block out the snoring noises of one's
partner, to help an infant sleep more soundly, or to drown out a
conversation you want to keep private! White noise can also be
used to determine the frequency response of mechanical
equipment.
The analogy with colors of light
does not stop with white noise. Another very commonly used kind
of noise is called 'pink noise'.
Instead of having equal energy at all frequencies, with pink
noise the energy within each successive octave is the
same, but it is reduced by 3 dB per octave,
i.e. each octave has half the power of the preceding
one. This is analogous to light that tends toward the red
or lower end of the visible light spectrum. Pink noise gives
more weight to the lower frequencies to compensate for the
increased number of frequencies of each higher octave. Also,
human hearing is most sensitive to sounds in the 1-4kHz range,
so pink noise makes the higher frequencies less prominent and
less hard on the ear. Some claim
that pink noise is the most common kind of noise found in
nature, e.g. the churning of ocean waves. Pink noise is also
often used for testing the frequency response of audio
equipment. You can produce white noise with a program to
generate random numbers, and you can turn white noise into pink
noise by filtering it ¡V though this is more difficult to do than
it sounds!
A less commonly referred to
'color' of noise is 'brown noise'.
This is supposed to simulate Brownian motion, a kind of random
motion that shifts in steady increments. 'Brown noise' decreases
in power by 6 dB per octave. Listen to a sample here. The
reverse of 'brown noise' is 'violet noise' (or 'purple noise'),
in which the power of each octave increases by 6 dB.
Brown noise in the news:
The Guardian, Wed 5 October 2022: ¡¥It
feels like fresh air to my ears¡¦: can brown noise really help
you concentrate?
https://www.theguardian.com/lifeandstyle/2022/oct/05/it-feels-like-fresh-air-to-my-ears-can-brown-noise-really-help-you-concentrate
There are still other 'colors' of noise,
but they are mostly curiosities, good for a little synaesthetic
fun, rather than being very practical concepts. Here are some
collections of a whole rainbow of
noise types:
http://en.wikipedia.org/wiki/Colors_of_noise
http://www.partnersinrhyme.com/blog/audio-tutorials/noise-types-and-colors/
http://www.wired.co.uk/news/archive/2011-04/7/colours-of-noise
Here is a more recent (Feb. 16,
2016) article from The Atlantic, entitled:
"The Many Colors of Sound: White noise isn't the only sonic hue
¡V
pink, blue, gray, and brown all affect listeners in different
ways:
http://theatlantic.com/science/archive/2016/02/white-noise-sound-colors/462972/
More
on the connection between the visual and auditory senses: The "Forry, Wrong Number"
unit of "A Moment of Science"
mentioned that, in addition to frequency cut-offs, a further
reason why it is difficult to hear some words clearly over the
phone is the lack of visual cues we get from watching
the face of the person talking. How much of a difference do
these really make in our understanding of speech? Go on to the
next page, and you may be surprised to see just how much
difference they can make!
Next: The McGurk Effect
(with
videos)