 |
 |
 |
 |
 |
 |
 |
What is white noise?
The adjective "white" is used to describe this type of noise because of the way white light works.
White light is light that is made up of all of the different colors (frequencies) of light combined
together (a prism or a rainbow separates white light back into its component colors). In the same
way, white noise is a combination of all of the different frequencies of sound. You can think of white
noise as 20,000 tones all playing at the same time.
Because white noise contains all frequencies, it is frequently used to mask other sounds. If you
are in a hotel and voices from the room next-door are leaking into your room, you might turn on a
fan to drown out the voices. The fan produces a good approximation of white noise. Why does that
work? Why does white noise drown out voices?
Here is one way to think about it. Let's say two people are talking at the same time. Your brain can
normally "pick out" one of the two voices and actually listen to it and understand it. If three people
are talking simultaneously, your brain can probably still pick out one voice. However, if 1,000
people are talking simultaneously, there is no way that your brain can pick out one voice. It turns
out that 1,000 people talking together sounds a lot like white noise. So when you turn on a fan to
create white noise, you are essentially creating a source of 1,000 voices. The voice next-door
makes it 1,001 voices, and your brain can't pick it out any more.
The adjective "white" is used to describe this type of noise because of the way white light works.
White light is light that is made up of all of the different colors (frequencies) of light combined
together (a prism or a rainbow separates white light back into its component colors). In the same
way, white noise is a combination of all of the different frequencies of sound. You can think of white
noise as 20,000 tones all playing at the same time.
Because white noise contains all frequencies, it is frequently used to mask other sounds. If you
are in a hotel and voices from the room next-door are leaking into your room, you might turn on a
fan to drown out the voices. The fan produces a good approximation of white noise. Why does that
work? Why does white noise drown out voices?
Here is one way to think about it. Let's say two people are talking at the same time. Your brain can
normally "pick out" one of the two voices and actually listen to it and understand it. If three people
are talking simultaneously, your brain can probably still pick out one voice. However, if 1,000
people are talking simultaneously, there is no way that your brain can pick out one voice. It turns
out that 1,000 people talking together sounds a lot like white noise. So when you turn on a fan to
create white noise, you are essentially creating a source of 1,000 voices. The voice next-door
makes it 1,001 voices, and your brain can't pick it out any more.
Your Sound Machine Review Authority
October 16, 2004
White Noise
Color-coding sound
During the summers when I was growing up, my bedroom had an air conditioner mounted in the
window. I loved the hot nights when I got to turn it on, but only partially because it cooled the room.
What I liked best was the sound, which I found to be very soothing. Years later, when I was in
college, I had a classmate everyone made fun of because he couldn’t go to sleep without having a
radio on next to his bed—playing static. For some reason, the sound of static on a radio seemed
goofy in a way that the sound of an air conditioner did not, but they amounted to roughly the same
thing: white noise, which has a well-known ability to promote sleep by masking other sounds.
Most of us have seen white noise generators or CDs of white noise that are sold as sleep aids—
sometimes especially for infants. A different class of white noise generator is used for testing and
calibration of pro audio equipment. But what exactly is white noise, how does it work, and why is it
called “white”?
Pure Noise
If you think back to elementary-school science classes, you probably learned that white light is a
combination of all the other colors of light; using a prism, we can separate it into its component
colors. By analogy, “white” noise is composed of sounds of every frequency within the range of
human hearing—roughly 20 to 20,000Hz (cycles per second)—with each part of the frequency
spectrum equal in amplitude (volume). It’s called “noise” instead of “sound” because it is random
in nature. Rather than simply generating a fixed tone at 20Hz, 21Hz, 22Hz, and so on all the way up
to 20,000Hz, a white noise generator creates a constantly changing mixture of tones such that all
frequencies have an equal probability of being audible at any given moment.
To human ears, white noise sounds like a hiss—sounds such as a waterfall, an aerosol can, and
static are all very similar to white noise. Although all frequencies are represented, we perceive
white noise as being relatively high-pitched—partly because higher octaves consist of a greater
range of frequencies than lower ones (giving the higher-frequency sounds proportionally more
energy), and partly because our ears are more sensitive to higher-pitched sounds.
White noise is good at masking most other kinds of sound because it effectively overloads or
“numbs” our auditory systems. Just as it’s difficult to hold a conversation at a crowded restaurant,
it’s difficult for your brain to identify any one sound or voice when you’re already hearing sound at
every frequency. So it’s not the white noise itself that promotes sleep as much as the fact that it
reduces audio clutter, drowning out other sounds that may distract you and therefore keep you
awake.
The Color of Sound
If “white” noise includes sound at every frequency, you might imagine it would be possible to
create other “colors” of noise by emphasizing certain ranges of frequencies over others. And you’d
be right. There is such a thing as pink noise, as well as red, orange, green, blue, purple, gray,
brown, and even black noise. Of these, pink noise is the most common—and the most clearly
defined. Whereas white noise has equal energy at every frequency, pink noise has equal energy
within each octave—in other words, the amplitude at higher frequencies is reduced to make it
sound more balanced to the human ear. Pink noise is used for, among other things, calibrating
speaker systems. The term “pink” signifies that it’s like white, but “tinted” or weighted toward the
lower-frequency (and therefore longer-wavelength) sounds. However, not all of the so-called noise
colors map onto the visible spectrum so clearly—and in any case, the color names are nothing
more than a convenient metaphor to describe white noise that has been filtered in various ways.
Many of the products claiming to produce white noise are recordings or simulations of wind,
waves, and other sounds that are in reality quite a bit more complex than white noise. Not that
there’s anything wrong with that—the sound of rain on the roof can be very soothing and can have
most of the same masking benefits as white noise. And just as the term “white noise” can be
stretched somewhat in meaning to include what you might call “off-white” noise, it also can have a
more metaphorical sense, as in “meaningless chatter.” But what I’d like to hear is a recording that
sounds just like my old air conditioner—complete with the hum that the compressor made every
time it came on. For me, that would beat a melatonin tablet washed down with a glass of warm
milk. —Joe Kissell
White Noise
Color-coding sound
During the summers when I was growing up, my bedroom had an air conditioner mounted in the
window. I loved the hot nights when I got to turn it on, but only partially because it cooled the room.
What I liked best was the sound, which I found to be very soothing. Years later, when I was in
college, I had a classmate everyone made fun of because he couldn’t go to sleep without having a
radio on next to his bed—playing static. For some reason, the sound of static on a radio seemed
goofy in a way that the sound of an air conditioner did not, but they amounted to roughly the same
thing: white noise, which has a well-known ability to promote sleep by masking other sounds.
Most of us have seen white noise generators or CDs of white noise that are sold as sleep aids—
sometimes especially for infants. A different class of white noise generator is used for testing and
calibration of pro audio equipment. But what exactly is white noise, how does it work, and why is it
called “white”?
Pure Noise
If you think back to elementary-school science classes, you probably learned that white light is a
combination of all the other colors of light; using a prism, we can separate it into its component
colors. By analogy, “white” noise is composed of sounds of every frequency within the range of
human hearing—roughly 20 to 20,000Hz (cycles per second)—with each part of the frequency
spectrum equal in amplitude (volume). It’s called “noise” instead of “sound” because it is random
in nature. Rather than simply generating a fixed tone at 20Hz, 21Hz, 22Hz, and so on all the way up
to 20,000Hz, a white noise generator creates a constantly changing mixture of tones such that all
frequencies have an equal probability of being audible at any given moment.
To human ears, white noise sounds like a hiss—sounds such as a waterfall, an aerosol can, and
static are all very similar to white noise. Although all frequencies are represented, we perceive
white noise as being relatively high-pitched—partly because higher octaves consist of a greater
range of frequencies than lower ones (giving the higher-frequency sounds proportionally more
energy), and partly because our ears are more sensitive to higher-pitched sounds.
White noise is good at masking most other kinds of sound because it effectively overloads or
“numbs” our auditory systems. Just as it’s difficult to hold a conversation at a crowded restaurant,
it’s difficult for your brain to identify any one sound or voice when you’re already hearing sound at
every frequency. So it’s not the white noise itself that promotes sleep as much as the fact that it
reduces audio clutter, drowning out other sounds that may distract you and therefore keep you
awake.
The Color of Sound
If “white” noise includes sound at every frequency, you might imagine it would be possible to
create other “colors” of noise by emphasizing certain ranges of frequencies over others. And you’d
be right. There is such a thing as pink noise, as well as red, orange, green, blue, purple, gray,
brown, and even black noise. Of these, pink noise is the most common—and the most clearly
defined. Whereas white noise has equal energy at every frequency, pink noise has equal energy
within each octave—in other words, the amplitude at higher frequencies is reduced to make it
sound more balanced to the human ear. Pink noise is used for, among other things, calibrating
speaker systems. The term “pink” signifies that it’s like white, but “tinted” or weighted toward the
lower-frequency (and therefore longer-wavelength) sounds. However, not all of the so-called noise
colors map onto the visible spectrum so clearly—and in any case, the color names are nothing
more than a convenient metaphor to describe white noise that has been filtered in various ways.
Many of the products claiming to produce white noise are recordings or simulations of wind,
waves, and other sounds that are in reality quite a bit more complex than white noise. Not that
there’s anything wrong with that—the sound of rain on the roof can be very soothing and can have
most of the same masking benefits as white noise. And just as the term “white noise” can be
stretched somewhat in meaning to include what you might call “off-white” noise, it also can have a
more metaphorical sense, as in “meaningless chatter.” But what I’d like to hear is a recording that
sounds just like my old air conditioner—complete with the hum that the compressor made every
time it came on. For me, that would beat a melatonin tablet washed down with a glass of warm
milk. —Joe Kissell
