Formula for Logarithmic (audio taper) pot
Although this question has been answered I just wanted to add something for those seeking an ideal logarithmic potentiometer law for simulation. A mapping from linear law to logarithmic law can be found in the general form:

$$ y = a\ b^{x} + c$$

Let this equation function define a mapping from \$0\leq x\leq1\$ to \$0 \leq y \leq 1\$, where \$a\$, \$b\$ and \$c\$ are free parameters to fit to desired curves. 

This is an equation with three free parameters so we can choose three constraints to derive the parameter values. For an ideal potentiometer, when the wiper is all the way to the minimum, the output should be no resistance, so therefore \$y=0\$ when \$x=0\$, and so
$$ 0 = a + c,\quad c = -a$$
So now we have the equation:
$$ y = ab^x - a.$$
Our second objective is to have maximum resistance when the wiper is all the way to the maximum, i.e. \$y=1\$ when \$x=1\$, so
$$ 1 = ab - a = a(b-1),\quad a = \frac{1}{b-1}.$$

Finally, we can choose a midpoint that we want the curve to go through, which I will leave as user definable as \$y=y_m\$ when \$x=0.5\$. This gives us
$$y_m = a(\sqrt{b} - 1) = \frac{\sqrt{b} - 1}{b - 1} = \frac{1}{\sqrt{b} +1}$$
and finally
$$ b = \left(\frac{1}{y_m} - 1\right)^2$$

This gives us a parametric logarithmic potentiometer law which can change the amount of curve. Bear in mind that when \$y_m = 0.5\$, \$ a = \infty \$. You could do a linearish map if you chose \$y_m = 0.5 - 10^{-5}\$ or something though (but why would you!).