You can destroy the transfer rate of a digital cable with the benign placement of a ferrite to lower RF. Maybe on the output cable of a switching power supply. However most manufacturers already have them. Bottom line it's a lot easier to do harm than good. RF is a real problem. The FCC is supposed to test all electronics for excessive RF, but that is little comfort to audiophiles who own sensitive gear. Think of the RF inside a desktop PC.(At least laptops run on batteries.) This is why a whole new component has emerged: AC filtering devices. They all have their pros and cons. There is many different technologies with every designer saying theirs is best. There is a good paper on Audioquest's site with the engineer eventually pushing his own.(I have a discontinued PS Audio Duet.) But don't put a ferrite or choke on your USB, coaxial, HDMI, etc. Toslink isn't a problem, but they have their own issues. Audioquest's Jitterbug and iFi's Silencer 3+ are good products for USB.
