[linux-audio-dev] scaling jackinput to dbSPL

Steve Harris S.W.Harris at ecs.soton.ac.uk
Tue Aug 15 14:09:11 UTC 2006

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.

Bob Katz advocates the "K-system" calibration, which is different again,
and also not very common.

- Steve

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