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

[Magnus Danielson]

From: Glen <mclilith at charter.net>
Subject: [sdiy] Formula for Audio & Log-taper pots?
Date: Wed, 14 Apr 2004 14:38:30 -0400
Message-ID: <4.1.20040414142320.024fd5a0 at mail.charter.net>,<4.1.20040414142320.024fd5a0 at mail.charter.net>

> 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.  ;)

The log tapered pots is really such that the pot-position needs to be sent
through an exponential function (exp() in C for instance) with propper
scaling prior and after.

You really only need linear and expo responses for most stuff. Pan-pots is
the exception IMHO.

A level pot should be exponential. Let's say that we have -80 dB to + 20 dB,
then we have (for the 11 positions from 0 to 10):

log       scale factor
+20 dB -> 10
+10 dB ->  3
+ 0 dB ->  1
-10 dB ->  0.3
-20 dB ->  0.1
-30 dB ->  0.03
-40 dB ->  0.01
-50 dB ->  0.003
-60 dB ->  0.001
-70 dB ->  0.0003
-80 dB ->  0.0001

Which is quite easy to do with an exp function and propper scaling. Fiddle
around with that and I'm sure you will find something usefull.

Cheers,
Magnus