[sdiy] Why dual grounds?

[David Ingebretsen]

Still working on this Steiner Synthasystem project...

I noticed on the keyboard schematic, Nyle very clearly uses 2 grounds. For
the life of me I don't see why. 

In general, why would one want two grounds in a circuit that is not a mix of
analog/digital and is not outputting signals for audio, just CVs?

Where and how would these two signals come back together. His power supply
is "nothing special", so to speak. Just one ground from the center-tapped
transformer, but he clearly runs these ground signals back to the power
supply somewhere.

No other module has two separate grounds.

So, why two grounds on this, but no other module?

I know you need to see the schematic, but I can't publish the thing. :(

David