YM3012 Analog Ground
The insides of the chip has many subcircuits, digital and analog, that may or may not have their grounds internally connected inside the chip. It is therefore the job of the chip user to connect all ground pins externally together to a common ground as shown in the diagram.

This is to have completely separate digital 5V supply for logic chips and analog +/- 12V supply for audio op-amps, so that digital return currents don't flow in the analog section ( or other way around). The digital 0V and analog 0V are only connected together at the YM3012 DAC.

That is just an example, you don't have to do it like that if you don't want to. You can just use single 5V supply and use opamps that work with single 5V supply.