Sony's CD player grounding strategies
Splitting planes is useful when there is common mode noise that creates large currents running on the ground plane. The split plane allows you to re-direct the current away from ground pins of the part.
If a current (especially a changing current) is running adjacent\past the ground pins it will create a small voltage from the resistance of the ground plane (there will also be a voltage created from any wires running back to the power supply).
A 5mA switching noise would create 10uV of noise if the resistance of the ground plane were 2mΩ (1oz copper is about 0.5mΩ, so 4 linear inches would be about 2mΩ)
There is no full schematic posted so I can't comment on the layout.
Also consider this: if you split the plane, you actually increase the resistance of the ground plane (especially if the current is run through a &quot;star point&quot; connector or jumper.)
A better way is to rearrange the components so large currents (returning back to the source through a ground in a power connector or to a supply mounted on the board) are directed away from sensitive parts. This can be done with proper layout.
Another thing that would help is to decrease the resistance of the ground by moving to a higher oz copper or larger grounding wires (going from 1oz to 2oz would decrease common mode noise by a factor of 2x).
Short story, don't cut the ground plane. It's almost never useful (there are a few cases where it is, isolation is one of those cases where it is useful). If you do cut the plane a good reason is to redirect large currents away from parts.