[Audacity-devel] Plot Spectrum, dB questions...

[Dominic M. <do...@mi...>]

Webb Phillips wrote:
> What is the frequency dialog? Is it the "Plot Spectrum" menu item? The
> "FFT Filter..." effect?

BTW, I just checked in a fix because the recent patch wasn't actually
correct.  Plot Spectrum now works again.

Is 20*log10(ratio) really the correct way to turn ratios of
sample values into decibels?  That would mean that the scale in
the Frequency window would have to go all the way down to -180 dB.
Is that correct???

Also it would mean that Amplify is using the incorrect conversion,
too.  Currently when you Amplify something by 10 dB, the spectrum
jumps up by 10 dB.  So at least they're consistent, even though
they may both be incorrect.

Can someone elaborate some more on when to use 10*log10(a) and when
to use 20*log10(a)?  Are there other audio programs which use
10*log10(a), which got me confused at some point?  Would someone
be willing to check all of our effects which claim to work with
decibels and see if they are using the correct formula
(empirically, not looking at the code)?

- Dominic