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 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’s going on here?

You might just need a simple ground loop isolator, like the $16 TII Network Technologies TII 220. Or if audible hum is your problem, the $80 EBTech Hum X will filter out the voltage in your ground line that’s causing it. Troubled by noise on your TV? An inexpensive ($10) Monoprice HDMI cable with a ferrite bead might do the trick. Yet another strategy is to plug all your gear into a line interactive uninterruptible power supply (UPS), such as the $250 Cyberpower CP1500PFCLCD.

Eliminate hum with the $80 EBTech HUM X

Or you can bring out the big guns and power everything with a high-end isolation transformer. If a device like the $510 Tripplite IS1000HG can be trusted to protect and clean up the electricity feeding hospital equipment, it should be good enough for your home theater gear.

The problem could be bad wiring, defective equipment, or just a noisy electronic environment. Whatever the type of noise you’re hearing—and whatever the cause—we’ll help you identify it–and then show you how to get rid of it.

Common problem 1: Ground loops

Ground loops are the number-one cause of unusual audio noise and weird video, 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 your home’s AC (alternating current) supply at different locations, and then connected together by electrical (versus optical) signal cables. RCA, HDMI, composite, component, and similar cables have shielding that’s connected to your home’s ground line. In the simplest terms, this creates a single-loop antenna that just loves to suck in various types of noise via electromagnetic induction. The illustration below shows how a ground loop can be created:

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.

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.

Resolve coax cable ground loops with the $16 TII Network Technologies' TII 220

If an extension cord is impractical, a hum eliminator such as Ebtech’s Hum X should do the trick, and there are other products that do roughly the same thing, some of which interrupt the loop in the signal cables. 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 less than $20.

Common problem 2: 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. 

Get pristine AC power with a Tripp Lite SU1000XLCD UPS

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 with a battery that’s 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 than the standby alternative, which keep switch to battery power on demand. Tripp Lite sent me its model SU1000XLCD UPS to clean up the super-dirty AC in my apartment. That device was selling for nearly $900 when I updated this article. It’s also heavy, about the 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 have nothing to do with noise elimination. But darn if it isn’t 100 percent effective at providing protection against power surges and outages. The Tripp Lite IS1000HG isolation transformer I mentioned earlier will also clean up AC line noise. It costs several hundred dollars less, but doesn’t provide battery backup power.

Condition your power with the Tripp Lite IS1000HG isolation transformer

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.

Common noise problem 3: Wires and cables

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 from a source device to self-powered speakers (i.e., not Wi-Fi or Bluetooth) are audio signal cables, not output cables.

Balanced audio cables, meanwhile, consist of three wires: Two wires are used carry the signal instead of one, but the polarity of that signal is reversed on one wire. The third wire is used for grounding. This design renders balanced cables far less susceptible to power-cable hum and other electrical noises. If your equipment provides the option of using balanced cables–whether they be XLR or TRS (Tip/Ring/Sleeve)–take advantage of it.

Speaker cables have far stronger signals traveling along them, so they shouldn’t be as affected by RFI. But just to be safe, try to keep your AC cords isolated.

Kill HDMI noise with a $10 Monoprice cable with a ferrite bead

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 or 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.

Common noise problem 4: 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 works as a Faraday cage.

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 gear needs protection from. I’m talking portable phones, cell phones, Wi-Fi equipment, and even computers.

Computers can generate a lot of RFI, which is why I shy away from cases with see-through plastic sides, which allow RFI to travel both ways. Wireless computer peripherals, such as mice and keyboards, can also cause interference. But 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, but it’s not a bad idea to keep your RFI-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 adequately shielded.

Common noise problem 5: 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 PC motherboard. Believe me: if my old ears can hear the difference, there is one. But when I first started using such gear, 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’s annoying.

There are three methods for removing USB (and HDMI) cable noise. One is to use a cable with a ferrite noise suppressor sleeve (a slug of iron molded around the cable). You can also buy clip-on ferrite noise suppressors. 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 audio component to your computer’s case. Speaker wire works fine for this. 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.

Kill cable noise by attaching ferrite beads

Common noise problem 6: 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 a computer’s 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.

The only good noise is the joyful noise you make

Any combination of the approaches shown above should 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 letters@techhive.com.

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