Reference Digital XLR 40 - Q. What happens to the signal which is outside of the audio band?
Answer:
The ferrite jacket has the effect of
attenuating external noise signals of 10 MHz and above that might reach
the audio signal. It would also attenuate radiation from the cable above
those frequencies from affecting other parts of the audio system. It
has no effect on the actual signal itself, other than to protect it from
radiated noise. It is similar to the ferrite ring that is sometimes seen
on USB and other computer cables, but is instead
distributed evenly throughout the jacket material rather than concentrated into one area. It is one of the factors that contributes to the low
measured jitter performance of the cable.