# (term) Signal-to-noise ratio

Discussion in 'Glossary of Terms' started by audiokid, Jun 6, 2010.

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1. ### audiokidChrisStaff

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Mar 20, 2000
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Signal-to-noise ratio (often abbreviated SNR or S/N) is a measure used in science and engineering to quantify how much a signal has been corrupted by noise.

It is defined as the ratio of signal power to the noise power corrupting the signal. A ratio higher than 1:1 indicates more signal than noise. While SNR is commonly quoted for electrical signals, it can be applied to any form of signal (such as isotope levels in an ice core or biochemical signaling between cells).
In less technical terms, signal-to-noise ratio compares the level of a desired signal (such as music) to the level of background noise. The higher the ratio, the less obtrusive the background noise is.

2. ### BoswellModeratorDistinguished Member

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Apr 19, 2006
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Some inaccuracies here. The S/N ratio is the ratio of the output power of a system with signal applied to the output power of the system without signal. It is usually expressed in dB. For example, a ratio of 1.5:1 (1.76dB) means that the contribution of signal power in the output is half as much as the noise, assuming the signal is uncorrelated with the noise. Only when you get to 2:1 (3dB) can you say that the signal power is as much as the noise power. For most audio (as opposed to communications) usage, we do not deal in power, and the ratio is applied to voltage, so it is necessary to be clear which definition is being used.

The term S/N ratio is also loosely (but incorrectly) applied to the concept of the ratio of maximum signal output voltage to the output voltage with no signal.

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