Most larger studios have a huge isolation trasformer for the whole set of studio circuits, and then smaller local filters like furmans. Balanced wiring as noted, also occasionally makes an appearance, but is less common. I run a dedicated ground. I personally use 3 transformers, and 3 filters (one capacitance, 2 mot). Not all in series mind you, but digital and analog gear are on seperate circuits, and a 3rd for hybrid designs (yay 80s synths). Analog recoding is sensitive to power in a huge way, but listening is seldom as affected. Note all studios use balanced audio, while most 'audiophile' crap is still unbalanced.