The phrase signal-to-noise ratio, often abbreviated SNR or S/N, is an engineering term for the ratio between the maximum possible signal (meaningful information) and the background noise. Because many signals have a very wide dynamic range, SNRs are often expressed in terms of the logarithmic decibel scale.
Due to the definition of decibel the SNR gave the same result independent of the type of signal which is evaluated (power, current, voltage).
SNR is also usually taken to mean an average signal to noise ratio, as it is possible that (near) instantaneous signal to noise ratios will be considerably different.
Higher signal to noise is better i.e. cleaner.
When using digital storage the number of bits of each value determines the signal-to-noise ratio. For n bit integers the dynamic range (DNR) is also determined. The formula is:
For floating point numbers, with n bits in the mantissa and m bits in the exponent:
Note: The SINAD is usually expressed in dB.
In common usage, "signal-to-noise ratio" describes the ratio of useful information to false or irrelevant information, for example in an online discussion forum.
Many Internet users prefer moderated forums, for instance, because moderation can improve the SNR of a forum. The Wiki collaboration model addresses the same question in a different way, by granting every user the power to "moderate" content. The assumption is that a majority of users are motivated by belief in the project goals, which leads to improved SNR by making it easier to add "signal" than "noise".