signal-to-noise ratio

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signal-to-noise ratio The ratio of the signal power to the noise power in a physical transmission channel; it is often measured in decibels (dB). The definition is best applied to statistically well-behaved noise such as white Gaussian noise. A more useful definition, frequently employed when small signals are needed, is signal-plus-noise to noise ratio. This has the benefit of being easy to measure. With large signals and low-noise circuits the two definitions are virtually identical. See also channel coding theorem.