Editing Signal-to-noise ratio (section)

==Noise reduction==
[[Image:Analyse thermo gravimetrique bruit.png|thumb|Recording from a [[thermogravimetric analysis]] device with poor mechanical isolation; the middle of the plot shows lower noise due to reduced human activity at night.]]

All real measurements are disturbed by noise. This includes [[electronic noise]], but can also include external events that affect the measured phenomenon — wind, vibrations, the gravitational attraction of the moon, variations of temperature, variations of humidity, etc., depending on what is measured and of the sensitivity of the device. It is often possible to reduce the noise by controlling the environment.

Internal electronic noise of measurement systems can be reduced through the use of [[low-noise amplifier]]s.

When the characteristics of the noise are known and are different from the signal, it is possible to use a [[filter (signal processing)|filter]] to reduce the noise. For example, a [[lock-in amplifier]] can extract a narrow bandwidth signal from broadband noise a million times stronger.

When the signal is constant or periodic and the noise is random, it is possible to enhance the SNR by [[Signal averaging|averaging]] the measurements. In this case the noise goes down as the square root of the number of averaged samples.