Speckmade: SNR moved to Signal-to-noise ratio

2007-06-13T16:17:50Z

← Older revision	Revision as of 16:17, 13 June 2007
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Pepoluan at 18:38, 9 October 2006

2006-10-09T18:38:20Z

New page

''Taken from [http://en.wikipedia.org/wiki/Snr wikipedia]''

'''Signal-to-noise ratio''' (often abbreviated '''SNR''' or '''S/N''') is an electrical engineering concept defined as the ratio of a given transmitted signal to the background noise of the transmission medium. It is also known as '''D/U ratio''', which stands for desired to undesired signal ratio.

== Technical sense ==

Signal-to-noise ratio is an engineering term for the power ratio between a signal (meaningful information) and the background noise:
:<math>
\mathrm{SNR} = {P_\mathrm{signal} \over P_\mathrm{noise}} = \left ( {A_\mathrm{signal} \over A_\mathrm{noise} } \right )^2
</math>

where '''''P''''' is average '''P'''ower and '''''A''''' is RMS '''A'''mplitude. Both signal and noise power are measured within the system [[bandwidth]].

Because many signals have a very wide dynamic range, SNRs are usually expressed in terms of the logarithmic [[decibel]] scale. In decibels, the SNR is 20 times the base-10 logarithm of the [[amplitude]] ratio, or 10 times the logarithm of the power ratio:

:<math>
\mathrm{SNR (dB)} = 10 \log_{10} \left ( {P_\mathrm{signal} \over P_\mathrm{noise}} \right ) = 20 \log_{10} \left ( {A_\mathrm{signal} \over A_\mathrm{noise}} \right )
</math>

=== Electrical SNR and acoustics ===

Often the signals being compared are electromagnetic in nature, though it is also possible to apply the term to sound stimuli. Due to the definition of [[decibel]], the SNR gives the same result independent of the type of signal which is evaluated (such as power, current, or voltage).

Signal-to-noise ratio is closely related to the concept of [[dynamic range]], where dynamic range measures the ratio between noise and the greatest un-distorted signal on a channel. SNR measures the ratio between noise and an arbitrary signal on the channel, not necessarily the most powerful signal possible. Because of this, measuring signal-to-noise ratios requires the selection of a representative or ''reference'' signal. In audio engineering, this reference signal is usually a sine wave, sounding a tone, at a recognized and standardized magnitude, such as 1 kHz at +4 dBu (1.228 V<sub>RMS</sub>).

SNR is usually taken to indicate an ''average'' signal-to-noise ratio, as it is possible that (near) instantaneous signal-to-noise ratios will be considerably different. The concept can be understood as normalizing the noise level to 1 (0 dB) and measuring how far the signal 'stands out'. In general, higher signal to noise is better; the signal is 'cleaner'.

Signal-to-noise ratio - Revision history

Speckmade: SNR moved to Signal-to-noise ratio

Pepoluan at 18:38, 9 October 2006