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signal-to-noise ratio


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Note added at 6 mins (2004-11-28 20:10:53 GMT)
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A New Standard for Acoustics in the Classroom (Trane Engineers ...
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Rita's answer is correct, but you might need some more explanation.
All the above are measured in decibel.
The decibel (dB) is used to measure sound level, but it is also widely used in electronics, signals and communication.
The sound level is measured in decibel, as well as the noise level - and their ratio, too. Somewhat surprisingly, there is no contradiction here, as decibel is a logarithmic quantity.
If you need to read more, please go to http://www.phys.unsw.edu.au/~jw/dB.html.


signal-to-noise ratio (SNR): The ratio of the amplitude of the desired signal to the amplitude of noise signals at a given point in time. [JP1] Note 1: SNR is expressed as 20 times the logarithm of the amplitude ratio, or 10 times the logarithm of the power ratio. Note 2: SNR is usually expressed in dB and in terms of peak values for impulse noise and root-mean-square values for random noise. In defining or specifying the SNR, both the signal and noise should be characterized, e.g., peak-signal-to-peak-noise ratio, in order to avoid ambiguity.

There's little to be added to Rita and Atilla's answers, except just to add a note of warning!

One would indeed perhaps expect 'snr' to mean singnal-to-noise' ratio in such an acoustic context.

HOWEVER

1) a value of 225 dB is almost unbelievably high for any practical system; one would almost suspect a typo for 22.5 dB, but that a value on the low side (though possibly appropriate for an ear defender).

2) Also, if this is referring to passive ear defenders, I fail to see (though my knowledge in this field is only peripheral) how a passive system can have a signal-to-noise ratio at all. The only interpretation I can imagine would be one of 'wanted-sound : unwanted-sound ratio'; but here again, the figure is unfeasibly high, and in any case, I don't know how a passive ear-defender makes any dfference between wanted/unwanted!

3) signal-to-noise ratio is more commonly (one might say more properly) written in lowercase letters: snr --- a nicety which however escapes most technical authors!

So I would be a little cautious in adopting this outwardly most logical solution.

My own feeling is that this might be referring to some other S... Noise Reduction --- like for example, 'Standardized Noise Reduction', and that there is in fact a typo for 22.5 dB. This could make sense in terms of sound reduction of 20 dB in H, M and L ranges being averaged out, weighted etc. to give a figure of 22.5 dB

Cf. NR [caps] for Noise Reduction factor figures in building acoustics

Presumably if you research the standard quoted, you ought to be able to find the intended meaning?

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Note added at 1 day 12 hrs 15 mins (2004-11-30 08:19:09 GMT)
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There you go! VPUhing has done the research, and I\'m utterly convinced that her/his answer is the authoritative one; though I still suspect a typo in that 225 dB?

SNR = 225 dB. Since it has a dB unit, it is not a ratio.

Check the following link for details:
http://argus-group.com/argus/pdf_files/NRR-SNR-formulas.pdf

http://www.argus-group.com/cgi-bin/miva?Merchant2/merchant.m...