Computers can generate a lot of RF, which is why I shy away from fancy see-through plastic sides which allow it both out and in. I’ve also heard wireless peripherals, such as mice, can cause interference. That’s a malfunction or bad design and the only fix is to replace them.
Back to the point: Don’t be paranoid about it, but it’s not a bad idea to keep your RF-emitting equipment as far away from your multimedia setup as you can. And if it’s a device that’s meant to be nearby, make sure it’s sufficiently shielded.
USB/HDMI cable noise
I use a $200 external USB audio interface because it sounds a lot better than anything you’ll find on a motherboard. Believe me, if my old ears can hear the difference, there is one. But when I first started using it, I would occasionally hear very faint static. For rather complicated reasons, current can leak into the shielding of USB cables which affects the signal. It was annoying.
There are three methods for removing USB (and HDMI) cable noise. One is to use a cable with a ferrite noise suppressor sleeve (that big round slug at one end. You can also buy a clip-on ferrite noise suppressor). These are sometimes called a ferrite bead.
The second method is to run a wire that’s less resistive than the USB/HDMI cable shielding from the case of the USB audio interface or HDMI-connected audio component to the case of your computer. Speaker wire works fine. Electricity always follows the path of least resistance, so spurious current runs down the ground wire rather than the cable’s shield. This is also known as a ground shunt, or simply a shunt.
The third method is to get a USB noise filter (I’ve never seen one for HDMI, but an HDMI adapter could work), which is actually a USB re-transmitter that splits the shield connection. These cost around $50 and are said to indeed eliminate the noise. I’ve never used one, because the first and second methods are far cheaper and have never failed me.
Once you heard it, now you don’t
Using the above methodologies, you should be able to eliminate all the noise that’s not inherent in your audio system, as well as some you might have thought was inherent. But if you’re suffering a type of noise that I haven’t covered, or have a home-brew fix that works, please share with us by leaving a comment, below.
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