(Three Different Noises, Three Very Different Fixes)
By Dawie Nolte · Nolte Productions
Not all noise sounds the same — and that’s actually good news. A low hum, a harsh buzz and a soft hiss almost always point to three completely different problems. Once you know which one you’re dealing with, the fix is usually not too complicated.
Show me a sound system that’s been running in a venue for a few years, and I’ll show you an operator who’s had at least one “what’s that noise?” moment. It’s one of the most common calls I get — some unwanted sound has crept into the system, nobody’s changed anything, and everyone assumes something is broken.
Here’s the good news: hum, buzz and hiss are three distinct problems with three distinct causes, and once you can tell them apart, tracking down the fix gets a lot less mysterious.
Three Noises, Three Very Different Problems
Before you reach for a screwdriver or a new cable, stop and actually listen to what the noise sounds like. I’ve seen a lot of hours wasted swapping out perfectly good gear because nobody paused to really listen first.
| Noise | What It Sounds Like | Usual Cause |
| Hum | A low, steady drone, around 50 Hz | Ground (earth) loop |
| Buzz | A harsher, more textured drone, often 100 Hz and up | Loose connection, damaged cable, or interference |
| Hiss | A soft, steady “sssh” with no clear pitch | Normal background noise from your equipment, made louder by incorrect volume settings |
Hum — Usually a Ground Loop
This is probably the most common type of noise that we come across, and it’s almost always down to something called a “ground loop.” It sounds technical, but the idea behind it is actually pretty simple. Every piece of equipment is connected to electrical earth (a safety wire that runs back to the wall socket), and it’s also connected to other gear through your audio cables. When two pieces of equipment are earthed at slightly different points, a faint current flows down the audio cable itself, which gets amplified right along with your audio — and comes out the other end as that steady, low-pitched drone, usually around 50 Hz, our mains electricity frequency here in South Africa.
Common causes:
- Equipment plugged into different power circuits or distribution boards
- Long cable runs between gear that doesn’t share a common earth
- Daisy-chained power strips, which create multiple paths to earth
- A poorly earthed wall socket or extension cord somewhere in the chain
Fixing It
- Where possible, plug all your audio equipment into outlets on the same circuit or distribution board.
- Use the ground-lift switch on a DI box (explained further down) for instruments or other unbalanced sources.
- For persistent cases, an isolation transformer (also called a hum eliminator) can solve it.
- Use good-quality balanced cables (more on this below) wherever you can.
One important safety note: never remove or defeat the safety earth on a mains plug to try to cure a hum. That earth connection exists to protect against electric shock. If you need to lift a ground, do it only on the signal cable — using a DI box’s ground-lift switch or a proper isolation transformer — never on the power cord itself.
Buzz — Usually a Connection or Interference Problem
Buzz is the harsher, more textured cousin of hum, and here’s the thing I tell people every time: it’s almost never your building’s electrical earthing. Nine times out of ten it’s something physical sitting in the signal path, and a bit of detective work will usually track it down fast.
Common causes:
- A loose or dirty cable connector, or a damaged joint inside the cable
- The wrong type of cable used for the job — for example, using a speaker cable as an instrument cable
- A faulty or aging cable with damaged shielding
- Dimmer switches or dimmable stage lighting running near audio cables
- Wi-Fi routers, cellphones, or other wireless devices placed too close to your cabling
A quick word on cable types: any cable carrying signal before it reaches an amplifier — mic, instrument, and mixer cabling — needs to be properly shielded, since those signals are weak and easy prey for interference. Speaker cable is a different animal: by that point the signal is much stronger, so it doesn’t need shielding, but it’s built with thicker conductors instead. Using the wrong one in the wrong place — especially a speaker cable feeding an instrument input — is a classic source of buzz. And cable quality matters more than people expect: a cheap cable with thin shielding or a badly soldered connector won’t just make you more prone to noise, it can dull your sound quality too. Good cable is one of the cheapest ways to protect everything else you’ve spent money on.
Fixing It
- Wiggle each cable and connector gently while listening — if the noise changes, you’ve found your culprit.
- Replace old, cheap, or visibly damaged cables.
- Make sure every cable ahead of your amplifier is properly shielded.
- Keep audio cables well away from lighting dimmer packs and power cabling; cross at a right angle where they must cross.
- Move Wi-Fi routers and other wireless devices away from your cable runs.
Laptops, PCs and That Charger Whine
If your noise problem appears the moment someone plugs a laptop or PC into the system, welcome to one of the most common calls I get. Laptop and PC chargers are switch-mode power supplies — they convert wall power to DC by rapidly switching current on and off, thousands of times a second. That switching gives off electrical noise, and if it finds its way into the audio path, you’ll hear it as a whine, buzz or hum that appears, or gets worse, while the charger is connected.
- Where practical, run the laptop off its own battery, and only charge it between sessions.
- If it must stay plugged in, try a different outlet or a different charger — cheap or third-party chargers are especially prone to this.
- Never take the laptop’s headphone output straight into a mixer channel over a long cable — use a DI box instead.
- Keep the laptop and charger physically away from microphone cables.
Balanced vs Unbalanced Lines (and Why DI Boxes Matter)
A lot of the noise problems in this guide come down to one underlying issue, and it’s a question I get asked constantly: “Dawie, why does my laptop buzz through the system, but the wireless mic doesn’t?” The answer almost always comes down to balanced versus unbalanced cabling — and this sounds more technical than it is.
Unbalanced Lines
Unbalanced lines send audio down a single wire, with the shield around it doing double duty as both noise-blocker and earth. That’s fine over a short distance, but the longer the cable, the more chances it has to pick up noise. Most instrument cables, laptop and phone outputs, and consumer RCA cables are unbalanced.
Balanced Lines
Balanced lines use a clever trick instead: the audio travels down two wires, with the second carrying an upside-down copy of the same signal. Any noise picked up along the way affects both wires equally — and when the mixer flips that copy back the right way up and combines it with the first wire, your actual audio gets stronger while the noise cancels itself out. It’s why XLR and balanced TRS cables shrug off hum and buzz over long runs, and why virtually all professional cabling is balanced.
Where the DI Box Comes In
A DI (Direct Injection) box bridges the two. I use one on almost every unbalanced source I run more than 4–6 metres. It takes an unbalanced signal — from a keyboard, laptop, or acoustic guitar — and converts it to balanced, so it can travel a long run without picking up noise. Most DI boxes also include a ground-lift switch, often the cleanest fix for exactly the kind of hum we’ve covered above.
Use a DI box whenever you’re sending a laptop, tablet or phone into the system, running an unbalanced instrument to the mixer, running any unbalanced source more than 4–6 metres, or chasing a hum that only appears with one specific source.
Hiss — Usually Not a Fault at All
Hiss is different in one important way: a small amount is completely normal. Every piece of electronic equipment produces a little of its own background noise, and hiss is simply that becoming audible.
It becomes a problem when the volume isn’t set correctly at each point between mic and speakers — something often called “gain staging.” If a signal starts too quiet at the mic preamp and gets pushed back up later at the fader, each stage adds its own hiss, and it all adds up by the time it reaches the speakers.
Fixing It
- Here’s how I approach it: set your fader to “0” (unity) first, then bring the gain up until you’re getting a healthy, solid level (assuming your amp levels are already set correctly). This naturally avoids both extremes — too little gain and you’re stuck down in the hiss, too much and you risk clipping, a harsh, crackly distortion.
- If you’re not using a tone control or effect, bypass it — every extra stage adds a small amount of noise.
- Cut, don’t boost, wherever possible.
A Quick Way to Track Down the Source
1. Solo (or mute all the others) one channel at a time, and listen for the noise in isolation.
2. On every channel? The problem is downstream — the amp, the wiring, or your building’s power. Only one channel? The culprit is in that channel’s own cables and gear.
3. Disconnect gear one piece at a time, starting closest to the source, and listen after each disconnection.
4. Wiggle cables and connectors gently — a noise that changes when you touch a point has found your problem.
5. If the noise changes when nearby lighting switches on, suspect interference rather than a wiring fault.
When to Call In a Professional
If the noise is tied to your building’s electrical wiring — it changes depending on which socket you use, or you feel even a slight tingle touching two pieces of gear — stop and call an electrician rather than an AV technician. At that point it’s no longer a sound problem; it’s an electrical safety issue.
Golden Rules
✔ Listen to the character of the noise before you start changing anything.
✔ Never defeat a safety earth to chase a hum — lift the signal ground instead.
✔ Get your gain right at the first knob (the mic preamp), not further down the chain.
✔ Keep audio cables away from power cables and dimmer packs.
✔ Replace old or damaged cables rather than nursing them along.
✔ If it’s tied to your building’s wiring, call an electrician, not just an AV technician.
What I’d Recommend
Next time something creeps into your system that wasn’t there before, resist the urge to immediately blame your gear. Listen carefully to what kind of noise it actually is — that alone will point you toward hum, buzz or hiss, and each one comes with a fairly predictable set of usual suspects.
A noisy system is almost never actually broken. Somewhere in the chain, something is either poorly earthed, loosely connected, or simply turned up in the wrong place — and all three of those are fixable.
Noise isn’t random — it’s information, if you know how to listen to it.
If you’re chasing a noise that won’t go away, or you’d like us to come out and do a proper system health check, we’re always happy to help.
— Dawie Nolte