dB

stefan · 7 Jul 2006

tecknoize wrote: Quick question... How do you calculate dB from a -1 to 1 magnitude range? 😕

First you need to find the amplitude of the signal, so take the absolute value of it. Then to convert a linear amplitude to a logarithmic (dB) one do: dB = 20 * log10(linearAmplitude)

tecknoize · 7 Jul 2006

Thanks (I think) it works! But how does software like FL or Cubase get a steady dB display when playing a sine wave for exemple? Do they analyse a small part to get the max dB of this part? I think I'm missing something... might be too tired 😮

stefan · 7 Jul 2006

tecknoize wrote: Thanks (I think) it works! But how does software like FL or Cubase get a steady dB display when playing a sine wave for exemple? Do they analyse a small part to get the max dB of this part? I think I'm missing something... might be too tired 😮

Analyse a small part would give you something similar to a RMS value. However, I'd recommend hooking the envelope follower up at the input signal, very short attack and long release (1-2 seconds) and then calculate the dB value from the output of the envelope follower.

Tom7777 · 7 Jul 2006

I recently had the need to do this myself, im guessing the same applys for 0-1 values right? can you do calculations like that with green data or would it have to be done in the code component? I don't do maths stuff much 😀

sambean · 7 Jul 2006

You'd want to do as little as possible with the steams/code to save cpu..

So what to do is take the signal you wan't to measure, attatch a mono to float, then do the rest in 'greens':

Signal->mono2float->abs module->x20->log10->dB

This has no smoothing though, to do this have a look in the 'Level meter' control in the toolbox, there's a green smoothie there... 😉

BTW devs, the level meter still hangs if it gets a #inf or #NAN value, and it's quite difficult to remedy if you don't know where the smooth module is.. Try feeding it a 1/0 signal to see..

Cheers

Sam

Tom7777 · 7 Jul 2006

Thanks Sambean 😀

stefan · 7 Jul 2006

Thanks sambean! Needs to be looked into!