Audacity Forum

The definition of dB is incorrectly documented. In the documentation, decibels are confused with bels. A change of 10 dB is a factor of 10, a change of 20 dB is a factor of 100, etc..
It would be good to know if simply the documentation is incorrect or the application's labels of the values used as well.

Can you give us a hint? There's a lot of documentation out there.
Koz

Sorry, I should have specified
I refer to the discussion below. best regards
-SL


http://wiki.audacityteam.org/index.php? ... aveform_dB
HowAudacityWorks
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Waveform dB
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Q: How is the waveform dB calculated?
A: See Wikipedia for full details. The basic idea is that dB is a logarithmic scale. If the sound amplitude (air pressure) goes up by a factor of 10 the dB goes up by one point. If it increases 100-fold then in dB it goes up by 2 and so on. This is very like the Richter scale for earthquakes. A one point change is a 10-fold increase in pressure.

An Audacity developer wrote that Wiki answer, but I am confused by it.

lord wrote:A change of 10 dB is a factor of 10, a change of 20 dB is a factor of 100, etc..

That's the power ratio, though. Audacity uses amplitude ratio, so a change of 10 dB is a factor of about 3, and a change of 20 dB is a factor of 10.


Gale

Yes, that is certainly faulty.
It isn't even true for Bel, since we are dealing with amplitudes and those are doubled by 6 dB and 10-fold by 20 dB. Or in linear terms: 0 dB = 1 and -20 dB is 0.1.

OK I attempted a "repair":
http://wiki.audacityteam.org/wiki/HowAu ... aveform_dB .

Thanks for the initial report.


Gale

Thank you Gayle for the correction.