[linux-audio-dev] scaling jackinput to dbSPL

[Dominique Michel]

Le Tue, 15 Aug 2006 14:03:34 -0400,
Paul Davis <paul at linuxaudiosystems.com> a écrit :

> > The db inside jack are dbFS with a maximum possible signal of 0 db.
> > Now, both jacqeq and jackmix give you a maximum conrol level at +6dB.
> > It mean at +6dB in those EQ is equal to 0dbFS in jack.
> 
> there are no dB units inside of JACK. some JACK applications use dBFS,
> that much is true. however, it is not true that because the allow a gain
> level of +6dB (or any value for that matter) that +6dB in that app
> equals 0dBFS. this is because JACK's floating point sample format allows
> values above 0dBFS, even though when such a value is passed to DAC, it
> will be clipped and caused distortion or worse.
> 
> within JACK, 0dBFS corresponds to a sample value of +/1.0, and will
> emerge from the other side of your DAC with the maximum voltage level
> that the DAC can emit. values above 0 dBFS are legal within JACK, but
> should probably never be routed to a physical output port.
> 
> --p
> 
> 
Thank you for this explanation.

Dominique