I also read that they use filtering devices, UPSs, etc.
Of course, industrial filters and UPSs are also used in studios when necessary, or in the case of UPSs, for fail-safe operation. If such a studio is located in an industrial area or in a city with an outdated power grid and an old tram or similar runs nearby, then this may be necessary.
For me, the server went down 2-3 times a day in an office in the middle of the city (a well-known large city in Germany), despite a normal off-line UPS, due to the disruptions and voltage fluctuations that occurred. Only a filtered online UPS with network conditioning solved the problem.
Incidentally, batteries also have their own noise that exceeds the noise of well-filtered SMPS. At this point at the latest, you can't gain anything and an SMPS is cheaper than batteries. There are special and very low-noise power supplies for high-quality notebooks, PCs and Macs for use in medicine, measurement technology, research, etc. This means that the devices are also less noisy than good notebooks with battery operation.
There are enough people (also known as audiophiles) who have converted devices or even entire systems to battery operation. In one expensive system that I heard, the owner had invested a high five-figure sum in a supposedly audio-compatible battery power supply with huge battery capacities, processing, etc. For what I heard, a system price of €5000 would have been a disgrace.
In the long run, almost everyone goes back to normal AC operation and has wasted a lot of time and money.
