Signal-to-noise ratio

The phrase signal-to-noise ratio, often abbreviated SNR or S/N, is an engineering term for the ratio between a wanted signal and background noise. Because many signals have a very wide dynamic range, SNRs are often expressed in terms of the logarithmic decibel scale.

Often the signals being compared are electrical (electromagnetic) in nature, though it is also possible to apply the term to sound and light stimuli.

In electrical systems it is usual to represent SNRs as an energy ratio, though in some circumstances they are represented as a voltage or current ratio.

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.

The SNR in decibels is 20 times the base-10 logarithm of the amplitude ratio, or 10 times the logarithm of the amplitude ratio.

Higher signal to noise is better i.e. cleaner.

SNR list:

Human ear = 150 db linear, Satellite single channel transmission = 133 db, O.C. 256 internet connection = 132 db, T1 internet connection = 123 db, P.C. hard drive recorder = 120 db, D.V.D = 106 to 120 db, V.H.S. tape = 100-110 db, high quality amplifier = 96 to 104 db, C.D. = 90 db, high quality turntable = 78 db, high quality tape deck = 52 to 78 db, high quality reel to reel = 45 to 72 db, MP3 = 45 to 64 db, F.M. radio = 42 db, 8 track tape = 34 db, A.M. radio = 31 db, home phone = 24 to 28 db, Cell phone = 2 to 24 db, human annoyance level = less than 17 db, human resolution limit wide (spectral) frequency = 2.5 to 40 db, human resolution limit single frequency = 0.9 to 3.4 db,

SINAD: Abbreviation for signal-plus-noise-plus-distortion to noise-plus-distortion ratio.

The ratio of (a) total received power, i.e. , the received signal-plus-noise-plus-distortion power to (b) the received noise-plus-distortion power.
The ratio of (a) the recovered audio power, i.e., the original modulating audio signal plus noise plus distortion powers from a modulated radio frequency carrier to (b) the residual audio power, i.e., noise-plus-distortion powers remaining after the original modulating audio signal is removed.

Note: The SINAD is usually expressed in dB.

Source: from Federal Standard 1037C in support of MIL-STD-188

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.

This usage appears to have originated on Usenet [What?? I don't believe this for a second. Usenet didn't even exist before the 1980s.], where off-topic posts and spam are regarded as "noise" that interferes with the "signal" of interesting discussion.

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".