When you see that barrel shaped piece of plastic covering a wire, usually towards one end or the other, have you ever wondered what it is and what it is used for?
It's called a ferrite bead or ferrite choke. They are used most often on video cables and USB cables. The choke is a passive filter, it has no power of its own and is simply a block of ferrite or iron powder with a thin wire coiled around inside it when it is formed or manufactured.
The wire or cable acts as an antenna and can pass noise or electronic signals through it to the components attached on each end of it, be it a television, monitor or a printer, even a DVD player. This noise can cause picture quality issues and loss of detail in a print job.
The image below illustrates how the noise interference shown as orange and yellow electrical signals is filtered out by the ferrite choke. The white hoop or ring in the center of the choke represents the choke and how it stops and holds the interference from reaching the device being fed the electrical signal.
Having a ferrite choke on a cable doesn't harm anything and in fact can actually help if the room you have your devices in has a lot of electromagnetic interference. Electromagnetic interference can be caused by a microwave, power lines and transformers on poles outside and inside a building, AM and FM radio signals, Wi-Fi broadcasts and cell phone signals.