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Noise consists of extraneous or unwanted
waveforms that can interfere with communication.
Although noise is most often associated with irritating
unwanted sounds, there is also noise that occurs in your
electrical lines and electromagnetic noise that can
interfere with radio communication. The signal-to-noise
ratio determines how much noise there is.
Questions you may have about noise are:
Sound noise
Any type of sound that interferes with
your normal hearing can be considered noise. It is often
loud and irritating. Some noise can also be quiet sounds
that you can barely hear but which interfere in the
desire for quiet.
Loud noises can interfere in being able
to hear conversation and other desired sounds. Noise can
inhibit the ability to concentrate or think and can even
cause health problems. Some people have to work in noisy
environments.
Examples of this type of noise includes
loud conversations, TV or radio that is too loud, and
loud vehicles.
Another example is wind noise in an
automobile. The shape of some cars will create the
rushing sound of air or even a whistling sound when the
auto is traveling fast, even with the windows closed.
This noise can be irritating, as well as to inhibit
listening to the radio or CD while on the highway.
Automobile engineers try to eliminate that noise.
There are times when a person wants
complete quiet. Subtle noises can be heard, which can
disturb the person. A TV in another room, a clock
ticking or someone talking quietly can be disturbing
noise to some people.
White noise is a type of random noise
similar to static. It is called white noise because it
consists of a full spectrum of waveform frequencies,
similar to how white light is a combination of a full
spectrum of visible colors.
Random waveform of white noise
Surprisingly, white noise can help
people fall asleep by masking other sounds, such as the
sound of a television in a neighboring room. It is used
in noise reduction. (See Noise Reduction for more
information.)
Electronic noise
Electronic noise can be either noise in
your electrical lines or static in electromagnetic
communications.
Your alternating current (AC)
electricity cycles at either 60 cycles per second (60Hz)
or 50Hz, depending on your country. Although this signal
starts off as a pure sine wave, it can pick up stray
waveforms from various electrical devices.
One example of electrical noise that is
added to your home current can be caused by a nearby
electric motor that may create an additional regular
signal, which can add to your normal AC signal.
AC waveform with noise added from
electric motor
Turning on a light will create a spike
in the waveform. Most electrical systems have filters to
protect the electronics from such small spikes. But if
lightning hits a power line to your house, there will be
a huge spike in the voltage. It can pop the circuit
breakers in your house. Such a large spike can also fry
the insides of your computer. That is why it is good to
have a surge protector in the electrical line to your
PC.
Thermal fluctuations in conductors can
create what is called Johnson Noise that can affect the
operation of sensitive electronics.
Electromagnetic waves include radio
waves, TV, and visible light among others. Electronic
noise is when outside signals interferes with signals
you want to receive. It is also called electromagnetic
noise.
One example of this is the static you
can hear on an AM radio during a thunderstorm. Every
time a lightning bolt flashes, static is heard on the
radio. FM stations are immune to this type of electronic
noise.
Another situation is the static you can
see on your television when someone is using an electric
hair dryer or mixer. The static noise seen on the screen
can be irritating.
Signal-to-noise ratio
A way to determine how much noise there
is can be determined by measuring the signal-to-noise
ratio (S/N).
The average amplitude of sound you want
to hear divided by the average noise amplitude will give
you the signal-to-noise ratio. Typically the noise is
not regular, thus you take its average to determine the
effect on the listener. When the S/N is 2 or less, it
starts to get difficult or unpleasant to hear the
sounds.
With AC electricity, your signal could
be 110 volts. In the picture above of the AC waveform,
the voltage of the noise is about 11 volts. Thus the
signal-to-noise ratio (S/N) is 10 (110/11), which is
very good.
Noise consists of unwanted waveforms
that can interfere with communication. It is often
irritating. Sound noise can be loud or even very subtle.
Electronic noise is often experienced in static in AM
radio and television. The signal-to-noise ratio
determines how much noise there is. |
