Non-periodic vibrations that are largely random and do not convey
a sense of definite pitch are called NOISE. WHITE NOISE
has an equal distribution of random energy per band within the range
of frequencies audible to the human ear. For example, there is the
same amount of energy between 100 and 200 Hz as there is between 6100
and 6200 Hz or between 15,700 and 15,800 Hz. This is the sound of
tape hiss, or the sound heard on a radio or TV channel after the station
assigned to that channel has left the air (the random "snow" seen
on the television screen can be thought of as the visual analog of
the white noise being heard.
PINK NOISE has an equal distribution of random energy per
octave within the range of audible frequencies. For example, there
is the same amount of energy between 100 and 200 Hz as there is between
200 and 400 Hz, 400 and 800 Hz, 800 and 1600 Hz, 1600 and 3200 Hz,
3200 and 6400 Hz, and 6400 and 12,800 Hz.
Relative to WHITE NOISE, the energy distribution of PINK
NOISE is more sparse in the higher frequency ranges and more concentrated
in the lower frequencies ( just as white light includes an even distribution
of frequencies of visible light, whereas red light consists primarily
of the lower frequencies of visible light). Examples of PINK NOISE
include the sounds of ocean waves crashing ashore, of distant thunder,
and of bass drums.
See NOISE,
GAUSIAN
NOISE from Barry Truax's Handbook for Acoustic Ecology.
