[linux-audio-dev] db gain controls.

[Jens M Andreasen]

On Fri, 2005-12-23 at 01:37 +0000, James Courtier-Dutton wrote:
> 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.

This would be the resolution of your fader. So next up: What is a
sensible resolution for a fader? Expensive well renomated equipment
appear to settle for 10bit (or approximately 0.1db if you prefer.)


> 
> 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?

Assuming 48K samplerate and a fader value (at most) every second ms

Left-shift your fader values as much as you can without loosing bits.
Interpolate the fader values over 96 samples.
Square them and average the most current 256 samples for smoothness

Multiply your signal.

> 
> James
-- 
mvh // Jens M Andreasen