[linux-audio-dev] db gain controls.

[David Kastrup]

James Courtier-Dutton <James at superbug.co.uk> writes:

> Hi,
>
> I have a question for some audio professionals out there.
> What is the smallest sensible gain control step in dB.
> Is it 0.5dB ?
> I am asking, because if one is using a digital gain control in a 24bit
> fixed point DSP, once could use almost any step size, so I am looking
> for the smallest sensible size to use.

Well, the minimum possible difference for 24bit is between -2^23+1 and
-2^23, and that would be about 0.000001dB.

> Some people mentioned earlier on a previous thread that there was
> something called soft gain control, where the user moves the gain up a
> step, but the mixer gradually(fairly quickly) adjusts the volume to
> the new level, so no clicks are heard on the speakers. How does these
> soft gain controls prevent the clicking? Do they wait for the zero
> crossing point to adjust the gain?

No, why should they?  You just ramp up the volume linearly.  If you
want to be even nicer, you use a shape that is even smoother.
Basically, you put the step pulse from the jump gain through a low
pass filter, preferably one that does not overswing.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum