Ferrite cores, also called beads or chokes, are used around the cables in audio or video equipment to shield them from electromagnetic interference. Simple cylindrical components, ferrite cores prevent interference both from and to a device.
Modern homes use a large number of electrical appliances that can interfere with each other. Many cables that carry signals, such as USB cables, already have ferrite beads installed along their length. Those who notice interference affecting the quality of their audio or video signals can add ferrite cores to shield unprotected cables. In audio systems, fitting them to speaker cables can remove most interference. However, users may need to fit an additional core to the power cord as well.