The overall effect of this expression is to "warp" the !Density fader such that is spends more of its throw at smaller numbers and only a small proportion of its distance is devoted to larger numbers.
The expression is actually (!Density * (0.666 inverse - !Density * -6.66) twoExp * 2 - 1), which would be equivalent to (6.66 * !Density) twoExp / 1024 * !Density (which is then scaled and offset to be in the range of [-1,1] so it can serve as the center value of the Noise).
For Density = 0, this would be 0 / 1024 * 0
For Density = 1, this would be 6.66 twoExp / 1024 * 1 = 0.098755153537997d
so the range is approximately [0, 0.1]
In other words, it changes the range of the !Density fader to 0.1, and warps it so more of its throw is spent at the smaller values.
I know you're already familiar with this, but for anyone else reading this who hasn't seen it yet, a good way to get a feel for what a Capytalk expression does is to:
- Select the Capytalk expression
- Use Ctrl+Y to evaluate it
- Move the faders so you can see the relationship between input and output values while watching an oscilloscope trace of the results.