[linux-audio-dev] scaling jackinput to dbSPL

conrad berhörster conrad.berhoerster at gmx.de
Tue Aug 15 15:27:59 UTC 2006

Whoow , that was fast....
maybe i was a little bit misunderstandable. 

when i wrote about jack, i meant the jackserver. i write an app, which has an 
microphon input. now i will take this microphon signal and show it as a gain 
meter. this is no magic and everything works. 

if i understand all of you right, the pressure on the microphon is something 
greater 0. and normally it is lower 2, right?
first question:  is this the same pressure which is measured in the literature 
in pascal (pa)
if so, its easy to calculate 
out_value = 20.00*(Math.log(in_value/0.00002)/Math.log(10.00));

I know, i need to calibrate the room at the end. But in the moment, my 
question is simply to get a signal and show the loundness in dbSPL.
Can i use the formula above or not? 

thanks c~

Am Dienstag 15 August 2006 16:09 schrieb Steve Harris:
> On Tue, Aug 15, 2006 at 03:30:47 +0200, conrad berhörster wrote:
> > Hello all,
> >
> > Does anybody know, how i can scale the incoming jack signals to dbSPL,
> > which is in the range of 0 to 120. An is it possible to calculate from
> > dbFS (which is used in normal soundapp in range -inf to 12db)  into
> > dbSPL.
> dB SPL is a measurement of physical sound energy, so in general software
> was no control over it. It depends on the efficientcy of your monitors,
> gain of your amps, desk etc.
> The only way you can relate dB SPL to dB FS is by calibrating your
> particular setup using a sound level meter. There's a SMPTE standard for
> the relationship between dB SPL and dBu or dBv (I forget which), which
> gets you half way there, but noone uses it anyway. I had my home system
> calibrated to SMPTE for a while, and it was just anoying.

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