Well, I have done blind testing.
Test conditions: wall (dedicated audio line with 12 AWG) with factory power cord, wall plus $2000 power cord, Plitron isolation transformer with factory cord, Plitron with $2000 cord.
The last two conditions were clearly better, and indistinguishable. So I spent money on isolation transformers.
Further, an isolation transformer also removes DC from the power line, which can really save your bacon (and your amplifiers) in a storm. So, if you have expensive gear, an isolation transformer is just reasonable care and insurance.
But they do tend to growl when working, so they should have a place outside the music room.
Test conditions: wall (dedicated audio line with 12 AWG) with factory power cord, wall plus $2000 power cord, Plitron isolation transformer with factory cord, Plitron with $2000 cord.
The last two conditions were clearly better, and indistinguishable. So I spent money on isolation transformers.
Further, an isolation transformer also removes DC from the power line, which can really save your bacon (and your amplifiers) in a storm. So, if you have expensive gear, an isolation transformer is just reasonable care and insurance.
But they do tend to growl when working, so they should have a place outside the music room.