[linux-audio-dev] scaling jackinput to dbSPL

James Courtier-Dutton James at superbug.co.uk
Tue Aug 15 23:35:46 UTC 2006

Dominique Michel wrote:
> Le Tue, 15 Aug 2006 12:01:11 -0400,
> Lee Revell <rlrevell at joe-job.com> a écrit :
>> On Tue, 2006-08-15 at 16:51 +0100, Dan Mills wrote:
>>> 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
>>> effects). 
>>> 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.  
>> FWIW, there is some work going on in ALSA to make the drivers use dB
>> units for the mixer, rather than arbitrary scales.  But of course this
>> will only work for devices for which the developers have the full
>> hardware specs.
>> Lee
> It is a good news.
> With jack, mixers as jackeq or jackmix are already using db scales.
> Dominique

ALSA is starting to support "dB Gain" indications for mixer controls. It
currently supports Creative Audigy cards and USB sound cards. Support
for other sound cards will follow in time.
So, at least people will know where the 0dB gain point is for the mic
and line in.


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