ROG Tonemender Vref explained?

[budjb]

Noob question here.

I've been looking at the tonemender schematic and the Vref stuff confuses me a bit.  From what I understand Vref is reference voltage, which seems like it would be a source of power.  However, in the schematic, there are a lot of places where it seems like it should go to ground but it ends up going to Vref instead.  Why is this, and what does that point do?

Edit: link for good measure http://www.runoffgroove.com/tonemender.html

[Ripthorn]

When working with opamps, it works on voltage swings that are relative to some voltage reference.  For example, in the tonemender, if you apply a +9V source at +Vcc and ground (0V) at -Vcc, then the reference voltage is one half that.  On the other hand, if you were to power the tonemender on +/-4.5V, then Vref, would simply be ground.  I forget the details of the opamps inner workings about this, but the point is that depending on how the supply voltage is defined relative to signal ground, Vref may or may not be ground.

[teemuk]

http://courses.cit.cornell.edu/bionb440/datasheets/SingleSupply.pdf