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Balanced vs Unbalanced Audio, and Why Your Cables Hum
What the third wire in an XLR actually does, why a two-metre guitar lead is fine and a twenty-metre one is not, and how to kill a hum without doing anything dangerous.
~8 min read · Updated August 2026 · By the Stage Supply team
In this guide:How it works · Connectors · DI boxes · Curing hum · Picks · FAQ
Balanced and unbalanced is one of those distinctions that sounds academic until the first time a stage hums through an entire first set. It is not academic. It is the difference between a cable you can run fifty metres across a venue and a cable that turns into an aerial after ten.
The good news is that the principle takes two minutes to understand, and once you have it, hum and buzz stop being mysterious.
What the third wire actually does
An unbalanced cable has two conductors: a signal core and a screen that doubles as the return path. A balanced cable has three: two signal conductors and a separate screen that does nothing but shield.
On a balanced connection the same audio is sent down both signal conductors, but one of them is inverted, so the two are mirror images. At the far end the receiving input flips one of them back and adds them together. The audio, being mirrored, adds up and gets louder. Any interference picked up along the way arrived on both conductors identically, so when one is flipped, the interference cancels itself out.
That cancellation is the whole trick, and it is why a balanced line can run a long way through a building full of lighting dimmers and mains cable without picking up a buzz.
| Unbalanced | Balanced | |
|---|---|---|
| Conductors | Signal and screen | Two signals and a separate screen |
| Typical connectors | TS jack, RCA, 3.5mm | XLR, TRS jack |
| Rejects interference | No | Yes, by cancellation |
| Sensible cable length | Up to about 5 metres | Tens of metres |
| Typical sources | Guitars, keyboards, laptops, phones, consumer gear | Microphones, mixer outputs, DI outputs, active speaker inputs |
The connector is a clue, not a guarantee
An XLR is almost always balanced. An RCA phono is always unbalanced. The jack is the troublemaker, because a TRS jack, with two rings on the shaft, might be a balanced mono connection or an unbalanced stereo one, and there is no way to tell by looking.
- A TS jack, with one ring, is unbalanced. Guitar leads are TS.
- A TRS jack on a mixer output or a monitor input is usually balanced mono.
- A TRS jack on a headphone socket or a laptop is unbalanced stereo.
- A 3.5mm mini jack is unbalanced stereo, every time.
Plugging a balanced output into an unbalanced input does not damage anything, it simply loses the benefit and often drops the level. The full connector reference is in pro audio connectors explained.
Where the DI box comes in
A DI box is the standard way to turn an unbalanced, high impedance instrument output into a balanced, low impedance signal the desk is happy with, at the point where the instrument is rather than at the desk. That last part matters: converting at the source means the long run across the stage is already balanced.
A passive DI uses a transformer and needs no power. It is robust, it sounds good on anything with a strong output, and it isolates the two sides electrically, which is why it is also the standard fix for a ground loop. An active DI needs phantom power or a battery and suits weak sources such as passive acoustic pickups, where a passive box can sound thin.
There is a fuller treatment in phantom power and DI boxes explained.
Curing hum and buzz, safely
Hum has two common causes and they sound different. A low, steady hum at mains frequency is usually a ground loop. A harsher buzz that changes when the lights change is usually interference getting into an unbalanced cable, or a dimmer sharing a supply.
Work through it in this order.
- Balance the connection. If a laptop or a keyboard is feeding the desk on a long unbalanced lead, put a DI box at the source. This fixes the majority of cases on its own.
- Shorten the unbalanced runs. Keep guitar leads and consumer cables as short as the stage allows, and do the long distance balanced.
- Separate audio and mains. Cross them at right angles rather than running them taped together down the same edge of the stage.
- Feed the whole audio system from one supply. Splitting audio across two different circuits is a common cause of loops, especially when the lighting is on one of them.
- Use the ground lift on the DI box. That switch exists precisely for this, and it breaks the loop on the signal side without touching anyone’s safety earth.
Never lift the mains earth
Removing or defeating the earth on a mains plug will often stop a hum, and it is a genuinely dangerous thing to do. The earth is what makes a fault safe. Use a DI box with a ground lift, which does the same job on the audio side, and leave the mains alone.
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Frequently asked questions
Is XLR always balanced?
In practice yes for audio, but the connector describes the plug, not the signal. A 3-pin XLR also carries DMX lighting data and intercom, which are not audio at all, so check what a socket is for before you patch into it.
How long can an unbalanced cable be?
About five metres is a sensible working limit, less if it passes near dimmers or mains. Beyond that you are relying on luck and a quiet venue. If a source needs to travel further, balance it at the source with a DI box.
Will a balanced cable fix a hum on its own?
It fixes interference picked up along the cable. It does not fix a ground loop between two pieces of equipment, which needs the loop broken, usually by the transformer in a passive DI or a ground lift switch.
Does balanced sound better?
Not by itself. It rejects noise, which usually means a cleaner result in a real venue, but a short unbalanced connection in a quiet room can sound identical. The benefit is immunity, not tone.
