[LAU] setBfree: Gain sweller from lin to log characteristic

Robin Gareus robin at gareus.org
Wed Dec 15 02:06:19 CET 2021

On 12/14/21 11:02 PM, Gerhard Zintel wrote:
> Now I have the following questions:
> Does anyone of you know if the original swell pedal of the B3 is 
> changing the volume in a linear or logarithmic way? 

Neither, and it is complicated.

Since the gain is applied before the pre-amp, many refurbished B3s use a
lamp and photo-cell/resistor to reduce hum, so any mapping is possible
there. But as far as I know, the original B3 uses a variable capacity to
control volume, which is linearly interpolating between 2 levels.

The pedal is connected mechanically via a rod, which connects to an arm
in the expression control. This adds some ratio. So while the electrical
control is linear, the overall throw is not.

Also as opposed to setBfree, many B3 pedals do not allow to go fully
silent, either.

> Maybe if the original B3 uses a linear characteristic we should not
> change setBfree's code.
There is also the problem that this would change existing projects that
use setBfree as plugin. Changing the expression pedal mapping will make
those sound different, so this is not an option.


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