I was thinking about using an external power supply for multiple pieces of analog audio gear. But it occurs to me that even if I use separate grounds for power and signal, because the wires would run alongside one another, changes in current on the power ground (from a power amplifier driving a 600 ohm load for example) would electromagnetically induce currents in the supposedly clean signal ground. Is this correct?
If yes, how can I model this in LTSpice? I assume it would just be two inductors coupled to some degree. Can someone explain roughly how to model EMI in long parallel wires?