How to get rid of hum and other noises from your audio, video systems

So you just unboxed your new entertainment gear, hooked everything up, and you hear a buzz, whine, hiss, chatter, or any number of other annoying noises that have been known to plague audio equipment. You might even see some banding or waves on your TV. So you take it all back to the store, only to watch the salesperson plug it in and have everything work perfectly. What the…?

I’d love to tell you that you did nothing wrong, but you may have, at least inadvertently. Then again, it could be bad wiring, defective equipment, or just a noisy electronic environment. Whatever the type of noise you’re hearing—and whatever the cause—here’s how to get rid of it.

Note: Some noise is inherent, such as tape hiss, or hiss when you turn up the gain on an input. It’s part of the equipment, and generally the only cure is… Better equipment.

Ground loops

The number-one cause of unusual audio noise and weird video is the ground loop, simply because it’s so darned easy to create. The most common manifestations are a loud buzz or hum coming through the speakers, or scrolling bands on a TV screen. It could also be a much quieter, yet equally annoying buzz or hum that you only hear when the room is otherwise quiet.

A ground loop typically occurs when one or more pieces of your entertainment system are plugged into the AC (alternating current) at different locations, then connected together by electrical (versus optical) signal cables—RCA, HDMI, composite, component—whose shielding is connected to ground. In the simplest terms, this creates a single-loop antenna that just loves to suck in various types of noise via electromagnetic induction. You can see how a loop is created in the diagram below.

Anything that breaks the loop will remove the noise, and the easiest way to do it is to power everything through a single AC socket. As shown below, simply plug all your equipment into a single power strip, surge protector, or power center and plug that  into the wall. Problem solved. Most multimedia setups can be handled easily by a single 15-amp circuit and most household circuits can deliver at least that.

There might be occasions where you simply can’t reach the same outlet with a piece of equipment. Self-powered speakers and subwoofers come to mind. You could just “pull the ground” by using a three-prong to two-prong adapter but this represents a potential shock hazard. Look up Les Harvey and Stone the Crows for an extreme example of what can happen with high-powered equipment.

If using an extension cord is impractical, you can buy a hum eliminator, such as Ebtech’s Hum X. But that costs $70. There are other products that do roughly the same thing, some of which interrupt the loop in the signal cables, but they’re all expensive as well. If you have the skills, you can build your own hum eliminator for about $10 or $15. You’ll find plenty of information online that will show you how, but the task requires moderate skill with a soldering iron and similar tools.

If those methods don’t fix things, the problem could be an over-the-air (OTA) antenna or a cable-TV coax cable that has its own path to ground. I’ve received some pretty annoying shocks when handling coax signal splitters. Normally—because of the isolation built into cable modems, cable boxes, and similar equipment—this will occur only if you’re connecting directly to the TV or to a video recorder.

If you’ve traced the problem to the TV signal wire that’s attached to a cable modem or similar (disconnect it and see if the problem goes away) replace that piece of equipment—there’s something wrong with it. If you’re connecting directly to a TV, there are ground-loop isolators available for $20 to $30.

AC line noise

Ground loops are hardly the only thing that cause electrical noise; pretty much any device with a motor (hair dryers and blenders, for instance), as well as dimmer switches and failing fluorescent fixtures will create this type of interference. It might be audible through your audio equipment or visible on your TV, or it might not. The obvious solution for this type of noise is to not use those types of devices while you’re watching TV or listening to music. You might be able to make that work—if you live alone. If there are other people under the same roof, perhaps not. 

If you’re willing to part with a few Benjamins, you can assure yourself of pristine AC without ground-loop noise by using a line interactive UPS (uninterruptible power supply) or an isolation transformer. A line interactive UPS is a battery-backup system whose battery is always engaged between the input AC and the output AC. This requires the electrical power to go through a conversion to DC (direct current) and then back to AC, which will remove all the noise.

Line interactive UPSes are more expensive. The SU1000XLCD UPS that Tripplite sent me to clean up my apartment’s super-dirty AC, for example costs about $600. It’s also heavy, about size of a small dehumidifier, and it has some features (such as USB monitoring, so that it can gracefully shut down an attached computer in the event of a power failure) that bear no relevance to noise elimination. But darn if it isn’t 100-percent effective at providing protection against power surges and outages.

It’s also much less-expensive than one of those high-end power conditioners you see marketed to gullible audiophiles. If you’re not worried about defeating ground-loop noise, you can get away for not much more than $100 with a UPS that advertises pure sine wave output.

Slightly cheaper than an online UPS, but absolutely effective against all kinds of line noise is an isolation transformer. Tripplite sent me one of these as well: the excellent 1000-watt IS1000HG (Hospital Grade) with four outlets. It’s about $500, but you can easily get away with a lower wattage (500 or 250) model for less than $250. Note that I’ve seen much cheaper on Amazon, but not from a known vendor, so I can’t vouch for them.

An isolation transformer is one of those products whose name describes it to a tee—it employs a special, shielded transformer that turns dirty AC into clean AC via electromagnetic induction—yes, the same thing that causes ground-loop noise.

Isolation transformers are designed for use with delicate diagnostic equipment, where even minimally noisy AC can cause spurious readings. That means they’re substantially more than adequate for multimedia setups.

Wires

There are really only one or two hard and fast rules for cables and noise. The first is to never run a power cable across or near audio or video signal cables, including antenna wires. Modern signal cables are well shielded, but if you’re getting hum and it’s not a ground loop, this could well be the cause. Note that the cables running to self-powered speakers (non-Wi-Fi) are audio signal cables, not output cables.

Also note that three-wire balanced signal cables (two signals, one with reversed polarity are sent—just like the famous humbucker pickup) are far less susceptible to power cable hum and other noise than two-wire cables. If your equipment gives you the option of using balanced outputs or inputs, XLR or TRS (Tip/Ring/Sleeve), do so.

Speaker cables, because of the far stronger signal travelling across them, shouldn’t be affected audibly. But just to be safe, try to keep your AC cords isolated.

The other rule for wires is not looping antenna signal cables (twin-lead), which tends to induce the same noise by making them antennas themselves. Electromagnetic induction; it’s a blessing, it’s a curse. (If you don’t know about it)

As to the quality of cables: A poorly made cable can cause noise issues, but there’s no real advantage to spending a fortune on them. A common misconception is that the more expensive the metal, the better the cable. Wrong. Gold is used on connectors because it doesn’t oxidize, not because it’s the best conductor of electricity. It’s quite good, better than nickel and chrome, but actually a bit worse than silver and copper. Forget platinum—it sounds sexy, but is about 20^th down the conductivity list.

Copper wire with gold connectors are the best combination; but again, don’t listen to the boutique audio sales propaganda. There are plenty of cables in the $10 to $20 range—or even lower—that will serve just as well.

One thing you could check for, though it’s mostly an issue in high-impedance (higher gain/voltage, aka Hi-Z) applications, such as with guitar cables, is that they aren’t microphonic. Poor or loose shielding and other factors can actually turn physical shocks into audio signal. I’m not kidding. I’ve experienced this only once in my life with component-connecting cables and that was for a turntable. But if you’re noticing odd noises that seem to be in time with the bass or vibrations, give the signal cables a hard tap with a finger (with the equipment powered on) to see if this is a problem.

One more wire issue: size. While larger gauge wire can actually help an amp work a little easier and cooler when driving speakers by lowering cable impedance (resistivity), the impact on signal cables is negligible. That is, it’s inaudible to anyone who didn’t pay a lot for a fat wire and needs to hear a difference.

RF interference

Ever wonder why the walls of your stereo receiver and other electronic devices are metal, when it seems like everything else in the world is made of plastic? It’s not for tensile strength, it’s to block incoming and outgoing RFI (radio frequency interference).  Any conductive material tends to block RF signals and shunt their charge to its surface. Indeed, the shielding on cables work as Faraday cages.

Since it wouldn’t be practical to turn your home theater into Faraday cage, you should instead look to lessen the strength of the radio signals your A/V needs protection from. I’m talking portable phones, cell phones, Wi-Fi equipment, and even computers.

Computers can generate a lot of RF, which is why I shy away from fancy see-through plastic sides which allow it to travel both ways. I’ve also heard wireless peripherals, such as mice, can cause interference. If that happens, it’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 near your setup, make sure it’s sufficiently shielded.

USB/HDMI cable noise

I use external USB and Thunderbolt audio interfaces because they sound 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.

PC audio noise

The other reason I use external USB and Thunderbolt interfaces is that they simply aren’t subjected to as much RFI. Internal audio solutions, especially those that reside on the motherboard, are susceptible to all sorts of line noise and electromagnetic interference that can’t be eliminated. As you might have noticed, I just gave you the solution—go external USB or Thunderbolt. That said, there are PCI and PCIe cards that might also eliminate the problem, as well provide more outputs for gaming and surround.

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 it with us by leaving a comment on our Facebook page and/or emailing me at jjacobi@pcworld.com.