Conclusions
The Internet is full of praise for these USB filters. The imagination works wonders here, equating USB and computers with noise, and assuming anything that filters it must make things sound better. That predisposition makes one perceive improvement even if it is not there.
Noise is easily measured as see above. So people should not assume a device is a true filter without seeing it actually measured as such. Based on this work, and confirmed by previous measurements I have performed, neither the Uptone Regen nor the TotalDAC D1 filter anything. Instead, they add their own noise components. Mind you, the addition while measureable, is not audible so no wonder no one is complaining about it. If you want to dismiss objective data on these products you can. But please go into any subjective review assuming that it could also do nothing versus "must be filtering."
It is in this context that I smile when I see the performance of the Intona USB Isolator. Finally a USB filter that actually filters! So congratulations to Intona for building a proper product that reproduces the USB bus cleanly.
Alas, as I have shown with RME ADI-2 DAC, you do not need USB filters. The solution to Modi 2 Uber noise and distortion is to buy a DAC at the same price or lower that doesn't have these issues. Schiit products seem to be sensitive to quality of USB power. Better designed DACs don't have that problem.
