Adjust volume curves?

[cyanidemonkey]

I have a crossfader on a 2 deck player I'm making.

I'd like to be able to adjust the crossfader curve like real mixers using a slider control. sliding it from a streight mix to a sharp/hard mix.

see graph below (streight mix - normal mix - sharper mix)

I currently have it doing a streight mix (left side image) using the following code to get a number between 0~100 from the crossfader slider ,converting it to decimal and multipling it by individual player volume, but am unsure how to make it adjust volumes like the other curves, which would make better mixes I think.

;convert 0~100 to 0.0~1.0
$xVolume = GUICtrlRead($crossfader)
    If $xVolume <> 100 Then
        If StringLen($xVolume) = 1 Then
            $xVolume = "0.0" & $xVolume
        Else
            $xVolume = "0." & $xVolume
        EndIf
    Else
        $xVolume = "1.0"
    EndIf

$crossfadeA = (1 - $xVolume)*(100 - GUICtrlRead($volumeA))
WMSetVolume($oDeckA, $crossfadeA)
$crossfadeB = $xVolume*(100 - GUICtrlRead($volumeB))
WMSetVolume($oDeckB, $crossfadeB)

Maths is not my stronge point, I figure it is a matter of getting a value from a curve adjust slider and doing something tricky to the $xVolume?