audio_tony
Addicted to Fun and Learning
Well this should get interesting then
Cambridge CEO response was pretty clear and professional, plus sounded good to me from an engineering explanation. But there are so many other posts on this thread that bring up other situations to obfuscate what appears to be a reasonable explanation.
Earth loops between a PC and DAC (with mains ground - not all have a mains ground) are a very real issue.
So often the USB port or PC motherboard is blamed for this noise, when in fact it's simply a ground loop and neither the USB port or motherboard is noisy (in a modern PC, noisy USB ports and boards are very, very rare and usually indicative of a fault elsewhere).
I performed various measurements using a Raspberry Pi, PC and a laptop.
The full tests are on my site here but the relevant spectrum graph is reproduced below - and as can be seen it looks remarkably similar to one of Amir's graphs (a noise curve has formed at -120dB rising in amplitude but then begins to drop off at around 10kHz where the ground loop effect begins to diminish.
