[linux-audio-dev] scaling jackinput to dbSPL

Dan Mills dmills_00 at yahoo.co.uk
Tue Aug 15 15:51:38 UTC 2006

--- conrad berhörster <conrad.berhoerster at gmx.de>

> 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));

Its not a case of calibrating the room, its basically
a case of needing to know what sample value 20uPa
equates to. 

This is dependent on the microphone, preamp and sound
card in use, or for the output case, the soundcard,
power amp gain and speaker sensitivity (plus room

You need to ensure that 120dbSPL at the transducer
does not clip either hhe mic, preamp or soundcard and
then find out what sample value this gives with your
hardware. Calibrate that point as 120dbSPL, then as
long as all your hardware is linear the rest of the
thing will just work. 

Regards, Dan.

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