Re: [linux-audio-dev] db gain controls.

On Fri, Dec 23, 2005 at 01:37:31AM +0000, James Courtier-Dutton wrote:

> 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.
>
> 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?

Steps of 0.5 dB would be smalll enough from a operational POV (except
mayby in equipment used to do A/B tests, where you'd want better than
0.1 dB).
The simplest way to avoid clicks is to interpolate the change over one
ore more periods (linear is OK if the step is small). This could still
give perceptible 'zipper noise' on some signals, so one step further
would be to lowpass the gain change at period rate, then interpolate
linearly.

-- 
FA