Virtual ground supply for audio-applications
All power supplies that are isolated from the power line will have some form of transformer.
There will be capacitance between primary and secondary of that transformer.
There will be &quot;displacement current&quot; coupled across that transformer.
That current will explore all possible paths, to return to the source of the charge.
Switching power supplies will produce 100 nanosecond edges (if not faster), and your opamp needs to harness that energy.
Or you must use bypass capacitors.
Otherwise ugly &quot;ground loops&quot; form, as that transformer-provided current makes its way back to the source.