Ferrites are best for high frequency noise, including radio stations and other EMI/RFI.
Their best use is if you have wall warts, like for your network, or Class D amps. They are good on fluorescent lamps, but man, they can put out so much noise that it's only a slight improvement there.
Their best use is if you have wall warts, like for your network, or Class D amps. They are good on fluorescent lamps, but man, they can put out so much noise that it's only a slight improvement there.