1. A Noise generator is a circuit that produces electrical noise (i.e., a random signal). Noise generators are
used to test signals for measuring noise figure, frequency response, and other parameters. Noise
generators are also used for generating random numbers.[1]
Shot noise
If electrons flow across a barrier, then they have discrete arrival times. Those discrete arrivals
exhibit shot noise. The output of a shot noise generator is easily set by the current. Typically, the
barrier in a diode is used.[3]
Vacuum diode
One common noise source was a thermally-limited vacuum tube diode. These sources can serve
as a white noise generators from a few kilohertz through UHF. Flicker (1/f) noise limits
application at lower frequencies; electron transit time limits application at higher frequencies.
The basic design is a diode vacuum tube with a heated filament. The temperature of the filament
sets the anode (plate) current that determines the shot noise. The plate voltage is set large enough
to collect all the electrons emitted by the filament.[4] If the plate voltage were too low, then there
would be space charge near the filament that would affect the noise output. For a calibrated
generator, care must be taken so that the shot noise dominates the thermal noise of the tube's
plate resistance and other circuit elements.
Forward-biased diode
Another possibility is using the collector current in a transistor.[5]
Zener diode
Reverse-biased diodes in breakdown can also be used as shot noise sources. Voltage regulator
diodes are common, but there are two different breakdown mechanisms, and they have different
noise characteristics. The mechanism are the Zener effect and avalanche breakdown.[6]
Reversed biased diodes that breakdown below about 7 volts primarily exhibit the zener effect;
the breakdown is due to internal field emission. The junctions are thin, and the electric field is
high. Zener breakdown is shot noise. The flicker (1/f) noise corner can be below 10 Hz.[7]
The decibel which is normally abbreviated dBA is the unit used to measure the intensity of a
sound. The human ear is incredibly sensitive, a person's ears can distinguish between wide
ranging sounds such brushing their fingers on a notepad to the loudest explosion or Jet aircraft.
To put these differences into perspective a jet aircraft is 1,000,000,000,000 times more louder
than the quietest audible sound.
Looking on the decibel decibel scale, the smallest audible sound which is near silence registers
at 0 dB. An increase of 10 decibels equates to a 10 fold increase in noise to your ear.

2. Noise Level Information
Important Point !!!!! Generators are measured and compared within the industry @ 7 metres.
To comply with EEC regulations all generators have to be marked in LWA this is a different
measurement of sound which is taken from a different distance. for an example a quiet Honda
EU20i is rated at its lowest at 52 dBA @ 7 metres on the LWA scale this would equate to approx
88 decibels. Please beware of this as all products have LWA marked on them, many do not have
the industry rated @ 7 metres level.
Here are some common sounds and their decibel ratings: