Most standard USB cables do not address RF issues and are fitted with filters that work over too narrow a range and are only fitted at the ends of the cables, leaving the length of the cable to act as an antennae.
iFi’s three custom-made metal oxide ceramic filters have a different effective range to broaden the range over which RF noise is silenced. The middle silencer is adjustable and can be moved along the whole length of the cable. This then “detunes” the antennae formed by the cable. The other two silencers should be kept as close to each respective end as possible.