Are there any measurements proving that these devices make a measurable difference?
I have seen one where some of these devices like the IFI or the Uptone reduced the noise floor on the USB slightly, but we are talking about -130db instead of -120db... So I don't think this would make any audible difference as the 120db was already far below any hearing levels... If it was something like -60db to -140db then yes that would be a big difference... but -120db to -130db not so much!
Unless you are having obvious problems with noise... Is there any proof these make an audible difference?
Maybe they do improve the sound, I don't know... Certainly they are interesting... But I have not seen any measurements confirming they do much?
Well think about it, you're talking about noise and jitter tests in reference to increased detail, soundstaging, and imaging through improved signal integrity and timing. A 12khz fft isnt going to show any of that, just like it isnt going to show the lack of information being rendered by slower tube amps compared to faster transistor amps, that information is lost forever in the slower amplifiers. Whats going to prove an audible difference? Actually being audible when listening. How could you actually see it? idk... maybe rerecord the output and analyse the millions of samples bit for bit.