When we state that an audio quality low noise linear power supply is useless in a pc playing a file with a somewhat perfect player, or we point out the uselessness of a reclocker or a USB port filter, because DAcs are already equipped with filters, we should specify and measure:
1) Which DAC
2) What is the percentage effectiveness of the filters and up to what EMI level, and if all the filters are all the same
3) Up to what EMI level there are no differences
When the scientists here present declare that it is useless to distinguish an audio pc from a common notebook, equipped with a lot of turbo fans, we should ask ourselves if in their measurements, the microphone and the equipment are able to detect the decibels emitted by the fans or the electric hum of the HD, mouse or display and how we can swear and certify that there are no differences!
This is real science!
Hang on a minute. Why do WE have to specify and measure everything about every product of a certain type, before we can claim that the class of devices is
largely useless? Every time these things ARE actually measured, through measuring the electrical output of a known good DAC with and without the product in the chain, there is no audible difference, and usually no difference at all, to be found. The same can be done at the output of the amplifier, and there is still no audible change.
Got that? Do you understand the implications of the output not being different?
So, it is not up to US to prove the claims, which often go way beyond EMI rejection, made for any of the products you list. It is up to those making the claims. But, once again, we have a "scientist" riding into the WIld West of audio, coming into town and shooting the concerned citizens and leaving the bad guys alone.
If you want proof that these products work, try taking it up with the manufacturers, get them to prove that their products work, directly, in the public arena via a clear measurement that can be repeated by somebody independent and via a proper double blind test. It is not Amir's job or anybody else's here to do that. In the spirit of investigation, every so often one of these devices gets tested, and the output doesn't change. There comes a point when our experts should be left to deal with products and techniques that do make a difference to the sound, surely?
Of course, if you have the capacity to do all those things you say, and access to the equipment to do it, you're welcome to try and prove that one of these products really is of value in an audio system at a given level of EMI (also proving that the practical working conditions in a home audio setup will ever reach that level of EMI pollution), and publish the test protocols and results here when you have that proof, so that anybody else can replicate the experiment and get the same result.
My guess is that we'll be waiting a long time for you to do that, though.