[sdiy] Formula for Audio & Log-taper pots?

[Henry Till]

Hi,

I've been working on a programming project where I
also need a "audio-taper" response on a gain control. 
The best I've found to do it this would probably be
this:

VSTs (and VSTis, for that matter) store parameter info
as 32-bit floats ranging from 0 to 1.  

To apply a "audio-taper" curve, you would raise these
parameter values (constrained between 0 and 1 of
course) to a given power somewhere around 2 or 3. 
When I plot this curve, it matches the curves I've
seen of audio-taper pots.  

While this seems to get the desired response, could
someone tell me if there is a more fitting formula to
use...

-Henry   


--- Glen <mclilith at charter.net> wrote:
> I need to explain to a programmer friend of mine the
> difference between
> linear, log, and audio tapered potentiometers. All
> the controls on his VSTi
> are linear taper, and some of them should definitely
> be either be audio or
> log taper instead. Explaining linear taper is so
> simple, I don't even have
> to do it.  ;)
> 
> I've read that audio taper pots have 15% resistance
> at the half-way point
> in their rotation, and that log taper pots have 10%
> resistance at the
> half-way point. Is this generally correct?
> 
> Does anyone know of a more precise way to describe
> the "curve" of either
> the resistance vs rotation, or more importantly, the
> attenuation vs
> rotation? I would really like to find a formula to
> calculate the
> attenuation for a given amount of rotation. I'd also
> be interested in a
> chart of the same data. I need something that will
> be crystal-clear to this
> programmer friend of mine. I'm not sure if just
> specifying the mid-point
> resistance would be enough for him to properly
> emulate a given taper.
> 
> Unfortunately, I don't have any loose pots laying
> around to make
> measurements of, at this time. So, I thought someone
> on the list might
> happen to know the answer.
> 
> thanks,
> Glen> 
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