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I am a EE, but haven't used these units much.

I do know that electrical power can be in peak values, or RMS average values. I don't know if this comes into play here.

But here is a units website that deals with dB values and there seem to be some agreement with these conversion, but you have to know if you are basing the conversion on peak (full scale), or average.

http://www.unc.edu/~rowlett/units/dictD.html

decibels don't have units, per se, but there are different scales.

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This comes into play when talking about gain of, say amplifier, since power ratio is a square of input/output voltage ratio

p1/p2=(v1/v2)^2

G=20log(y/x)[dB]=2x10log(y/x)=10log(y/x)^2[dB]

Something like that (its been decades..)

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Bonjour Etienne,

deziBel denote ratios of two measurements of equal kinds. Such ratios are dimensionless (or unit-free). So no problem with a logarithmic scale. Confusing - maybe. But useful e.g. assessing noise, amplifiers, damping, etc.

Edit: The factor on page 75 must be 20, of course. Thanks for pointing to that! Will be corrected in next edition. Merci!

*Edited: 21 Sept 2011, 2:44 a.m. *