Control audio-out volume as curve, not linear

Hey Guys,
really hope somebody can give me a hint on this one:

I need to control the volume of an Audio-Out node related to a linear input in a non-linear way.

My input value is a floating number between 0.0 and 1.0. Normally I could simply map it to my output value of -100 dB to 0 dB. Drawn as a mathematical graph, this would show as a straight rising line.

But this time I would prefer to create a different behavior:
When beginning to raise the input value (eg. between 0.0 and 0.3) there should be a significantly stronger increase in volume than when raising the value at the end of the input scale (eg. between 0.7 and 1.0). As a graph this would be a curve similar to this one:

How can I do this? Is there maybe even a way to create a GUI element similar to curves-control in Photoshop to control my curve?
Any suggestions are highly appreciated…

If you add a Gamma node (and press F1 for the help file), it will do just that.

also, someone made a module containing a load of different Tweens/transition curves, if Gamma does not suit your needs…
found it via google:

Its even done as a plugin by west:

why you dont use EXPR node, and input de ecuation…

wow - tons of answers!
Right now I implemented the Gamma node, but I will check out the others as well, THX!

anybody wishing to do more complex stuff could still implement the diagram at :)