[linux-audio-dev] scaling jackinput to dbSPL

Paul Davis paul at linuxaudiosystems.com
Tue Aug 15 18:03:34 UTC 2006

> 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.


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