Mains Hum & Ground Loop Tester

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Identify the electrical hum or buzz in your audio system. Play a reference 50 or 60 Hz mains hum and match it by ear — no microphone needed.

Low-frequency tones can be louder than they seem and may stress small speakers. Start quiet and raise the volume gradually.
Mains frequency ?Pick your local mains frequency. 60 Hz covers North and most of South America and parts of Asia; 50 Hz covers Europe, most of Asia and Africa, and Australia.
Sound ?Pure tone is a clean reference. Hum (50/60 Hz) is loudest at the line frequency — the sound of induction or a ground loop. Transformer hum is loudest an octave up (100/120 Hz) — a transformer core or power supply. Buzz is the harsher, harmonic-rich sound of a light dimmer.
60 Hz
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About This Tool

This tool plays a synthesized reference of mains hum — the low electrical drone and buzz that creeps into audio systems — so you can match it by ear and pin down what you are hearing. It runs entirely in your browser with no microphone and no setup. You choose your mains frequency and the character of the sound, and your own ears do the comparing, exactly as an engineer does when chasing hum on a bench.

How to Use

  1. Choose your mains frequency (50 or 60 Hz) and a sound: pure tone, hum, transformer hum, or buzz.
  2. Press play and compare the reference with the noise coming from your system.
  3. Once you have identified it, use the safe fixes — balanced connections, an isolation transformer, single-point grounding.

Methodology

Mains hum is tied to the alternating current in the power line. Its audible pitch is usually twice the line frequency — 100 Hz where the mains runs at 50 Hz, and 120 Hz where it runs at 60 Hz. That doubling happens because the magnetic force in transformer cores peaks twice per cycle (an effect called magnetostriction), and the ripple from full-wave power supplies does the same. The result is a tone an octave above the mains frequency, rich in harmonics. But not every mains hum sits at that doubled pitch. Hum from magnetic induction and ground loops — where stray line-frequency fields drive a current around the loop — is loudest at the line frequency itself, 50 or 60 Hz. That gives a useful rule of thumb: a hum at the line frequency points to induction or a ground loop, while one an octave higher, at 100 or 120 Hz, points to a transformer or a power supply.

Sources: Wikipedia — Mains hum · Wikipedia — Magnetostriction · Wikipedia — Utility frequency · Whitlock — Hum & Buzz (Jensen AN-004)

Understanding Your Results

Match the noise in your system by ear. If it is loudest at the line frequency (50 or 60 Hz), try Hum (50/60 Hz) — a sign of magnetic induction or a ground loop. If it sits an octave higher (100 or 120 Hz), try Transformer hum — a sign of a transformer core or a power supply. Use Pure tone to tell 50 Hz from 60 Hz, and Buzz for the harsher, harmonic-rich noise of light dimmers and similar switching gear. If nothing locks on, the noise may be hiss or interference rather than mains hum.

Sources: Wikipedia — Ground loop · Wikipedia — Mains hum

Practical Examples

On 60 Hz power you hear a deep drone. You select 60 Hz and Transformer hum, and the tone — loudest at 120 Hz — matches, confirming hum from a transformer or power supply rather than hiss. A different hum appears only when your audio interface and laptop are both connected — a classic ground loop. With Hum (50/60 Hz) selected, the 60 Hz tone matches. A balanced cable or an isolation transformer clears it, with the mains earth left safely in place.

Tips for tracking down hum

• Cure a ground loop in the signal path, not the power cord: use balanced (differential) connections, an isolation or hum-eliminator transformer, or reference everything to a single grounding point. • Never disconnect the mains earth — lifting the third pin or using a cheater plug can silence hum but creates a real electric-shock hazard. • Keep signal cables away from power cables and power supplies, and try unplugging devices one at a time to find the culprit. • Set the volume to match the hum you hear; a fair loudness makes the comparison much easier.

Sources

All calculations are performed locally in your browser. No data is sent to any server.

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Frequently Asked Questions
Is my hum 50 Hz or 60 Hz?
It depends on your region's mains frequency. 60 Hz is used across North America, most of Central and South America, and parts of Asia (such as Korea, Taiwan, and the Philippines). 50 Hz is used across Europe, most of Asia and Africa, and Australia. Play both and see which one locks onto your hum.
Why does my 60 Hz hum actually sound like 120 Hz?
Because the audible part of mains hum is usually twice the line frequency — 100 Hz on 50 Hz power, 120 Hz on 60 Hz power. The magnetic force in transformer cores peaks twice per cycle (magnetostriction), and the ripple from full-wave power supplies does too, so the loudest tone sits an octave above the mains frequency.
What if my hum is at 50 or 60 Hz, not 120 Hz?
A hum loudest at the line frequency usually comes from magnetic induction or a ground loop, rather than a transformer or power supply — those hum an octave higher, at 100 or 120 Hz. Match it with the Hum (50/60 Hz) sound, then fix it in the signal path with a balanced connection or an isolation transformer — never by removing the mains earth.
What is a ground loop?
A ground loop happens when two pieces of equipment are connected to ground through more than one path, and those paths sit at slightly different voltages. The difference drives a small current around the loop, which you hear as hum. It is common when two mains-powered devices are linked by a signal cable whose shield grounds both chassis.
How do I get rid of mains hum safely?
Use balanced (differential) connections where you can, add an isolation or hum-eliminator transformer in the signal path, and reference everything to a single grounding point. Keep signal cables away from power cables. These remove the loop without compromising electrical safety.
Doesn't lifting the ground pin stop the hum?
Disconnecting the mains earth (lifting the third pin or using a cheater plug) can reduce hum, but it removes the protection that prevents electric shock and is genuinely dangerous. Never do it. Break the loop in the signal path instead — with balanced connections or an isolation transformer.
Do I need a microphone?
No. The tool generates reference tones and plays them through your speakers or headphones — it never listens or records. You compare what you hear with the noise in your system by ear.
Can I use headphones?
Yes, headphones are fine for matching the pitch and character of the hum. Bear in mind that the hum you are chasing usually comes through your speakers and equipment, so you may want to A/B against the real system as well.
Is any audio or data sent anywhere?
No. Every tone is generated on your device and played locally. Nothing is recorded, uploaded, or stored, and the tool keeps working offline once the page has loaded.