signal-to-noise ratio

The ratio of the power or volume (amplitude) of a signal to the amount of disturbance (the noise) mixed in with it. Measured in decibels, signal-to-noise ratio (SNR or S/N) measures the clarity of the signal in a circuit or a wired or wireless transmission channel. See interference-to-noise ratio.

The Larger the Number, the Better
The greater the ratio, evidenced by a larger number, the less noise and the more easily it can be filtered out. The lowest number is an SNR of 0, which means that noise and signal levels are the same. Although signals contain non-random intelligence and can be isolated and separated, with a 0 SNR, it would be extremely difficult to isolate the signal in real time. It would be more easily accomplished offline.

As a Metaphor
The terms "signal" and "noise" are also used in chat rooms and Usenet discussions to refer to meaningful discourse (signal) versus worthless blather (noise). It also describes the results obtained from a search engine, where the signal (relevant information) is very small compared to the noise (useless information).

signal-to-noise ratio [′sig·nəl tə ′nȯiz ‚rā·shō]

(electronics)

The ratio of the amplitude of a desired signal at any point to the amplitude of noise signals at that same point; often expressed in decibels; the peak value is usually used for pulse noise, while the root-mean-square (rms) value is used for random noise. Abbreviated S/N; SNR.

Signal-to-noise ratio

The quantity that measures the relationship between the strength of an information-carrying signal in an electrical communications system and the random fluctuations in amplitude, phase, and frequency superimposed on that signal and collectively referred to as noise. For analog signals, the ratio, denoted S/N, is usually stated in terms of the relative amounts of electrical power contained in the signal and noise. For digital signals the ratio is defined as the amount of energy in the signal per bit of information carried by the signal, relative to the amount of noise power per hertz of signal bandwidth (the noise power spectral density), and is denoted E_b/N₀. Since both signal and noise fluctuate randomly with time, S/N and E_b/N₀ are specified in terms of statistical or time averages of these quantities.

The magnitude of the signal-to-noise ratio in a communications systems is an important factor in how well a receiver can recover the information-carrying signal from its corrupted version and hence how reliably information can be communicated. Generally speaking, for a given value of S/N the performance depends on how the information quantities are encoded into the signal parameters and on the method of recovering them from the received signal. The more complex encoding methods such as phase-shift keying or quadrature amplitude-shift keying usually result in better performance than simpler schemes such as amplitude- or frequency-shift keying. As an example, a digital communication system operating at a bit error rate of 10^-5 requires as much as 7 dB less for E_b/N₀ when employing binary phase-shift keying as when using binary amplitude-shift keying. See Electrical communications, Information theory

1.	(communications)	signal-to-noise ratio - (SNR, "s/n ratio", "s:n ratio") "Signal" refers to useful information conveyed by some communications medium, and "noise" to anything else on that medium. The ratio of these is usually expressed logarithmically, in decibels.
2.	(networking)	signal-to-noise ratio - The term is often applied to Usenet newsgroups though figures are never given. Here it is quite common to have more noise (inappropriate postings which contribute nothing) than signal (relevant, useful or interesting postings). The signal gets lost in the noise when it becomes too much effort to try to find interesting articles among all the crud. Posting "noise" is probably the worst breach of netiquette and is a waste of bandwidth.