Audio Output Levels between Applications

Right, hoping this doesn't sound like a terribly stupid question or something (which I'm guessing it is), but is there any way to control the sound levels from different applications within my Mac?

My problem is that when using Reason, I hear a noticeable difference in volume when then playing something on iTunes for example, or using the internet. Is there any way I can control these different volumes so I don't have to keep turning the Mac's volume down every time I switch program?
Any feedback would be appreciated
Tom