In this guide
An audio hum or buzz is almost always caused by a ground loop — a difference in electrical potential between two pieces of gear that forces a small current through your audio cables, producing a 50 or 60 Hz hum (or a harsher buzz at harmonics).
- All devices share the same AC outlet or power strip
- You use shielded cables such as XLR throughout
- A ground lift adapter, DI box, or transformer-isolated USB audio interface breaks the loop
- RF or wireless devices are kept away from audio cables
- Devices plug into different outlets with differing ground potentials
- Cables are unshielded or damaged, picking up EMI
- A laptop or computer switch-mode power supply is injecting noise
- The safety ground is lifted at the wall — a shock hazard, not a real fix
What Is a Ground Loop?
Every AC outlet has a ground wire. When two devices plug into different outlets, even in the same room, those grounds can sit at slightly different voltages. Connect the devices with an audio cable and you create a loop — current flows around it and your speakers or headphones reproduce it as a steady hum. This is the cause behind the vast majority of audio hum or buzz complaints.
Common Sources at a Glance
| Setup | Works? | Need | Note |
|---|---|---|---|
| All gear on one power strip | Yes | Nothing extra | Equalises grounds immediately |
| PC + audio interface on different outlets | No | Same outlet or DI box | Most common laptop hum scenario |
| XLR balanced cables used throughout | Yes | Balanced outputs on gear | Common-mode rejection kills hum |
| Unshielded RCA cables near power cables | No | Shielded cables + re-route | Picks up EMI and RF |
| Transformer-isolated DI box in signal chain | Yes | DI box | Breaks loop without lifting safety ground |
How to Fix Audio Hum Step by Step
- Plug everything into one strip. This is the free first step — try it before buying anything.
- Swap to shielded or balanced cables. XLR cables reject interference that unshielded RCA cables absorb.
- Add a DI box or isolation transformer. These break the ground loop in the signal path without touching the safety ground.
- Use a transformer-isolated USB audio interface if a laptop power supply is the culprit — choosing the right USB audio interface makes a real difference here.
- Move RF sources. Phones, Wi-Fi routers, and fluorescent lights near cables can cause buzz. Reroute cables or add an RF filter.
For a deep-dive into the engineering behind ground loops, ProSoundWeb’s hum troubleshooting guide is the most thorough free resource available.
When It Is Not a Ground Loop
If the hum persists with nothing connected to the input, the fault is inside the device — a failing capacitor or noisy internal power supply. If it only appears with a specific cable, that cable is damaged or poorly shielded. Video-over-cable setups can also introduce noise into nearby audio runs; if you recently added a display adapter, see our guide on why USB-C to HDMI sometimes fails for related signal-integrity tips.
Bottom line: Start by plugging all your gear into the same power strip — that alone clears most audio hum or buzz. If it persists, move to shielded or balanced cables, then add an isolation DI box. Never lift the safety ground at the wall outlet to solve hum; it removes your shock protection without reliably fixing the noise.