Remove hum from audio
Reduce 50 or 60 Hz hum and its first four harmonics in your recording. Compare before and after, free in your browser with no audio upload.
Never uploaded. Everything runs in your browser.
What's happening
Hum is a low, steady buzz under the voice. Mains interference can enter through a ground loop, a nearby power lead or another device in the setup. It commonly sits near 50 or 60 Hz, with higher harmonics. Other equipment can produce tones at different frequencies, so a buzz alone does not identify the faulty connection.
fix.fm looks for narrow peaks and compares their level with louder speech. Its warnings increase at 40, 30 and 20 dB below the voice; audibility also depends on playback and the recording. Compare hum with hiss and room echo before choosing a fix.
How far the hum fix goes
The hum fix is built for one thing: a steady mains tone and its first harmonics. Not every low sound under a voice is that. The three cases below are the same clean reading with a different low background added in software, so we know what was there and can measure what came out, what was left, and whether the voice paid for it.
One clean reading with three low backgrounds added in software, then run through this page's fixer at full amount. Every clip is matched to -23 LUFS so only the background differs.
Clean reading
The reference. The pauses are empty; the low end is the voice and nothing else.
Mains hum, 22 dB under
A ground loop as the fixer models it: 60 Hz and four harmonics. A steady low note under everything, clearest in the pauses.
Mains hum, after the fix
The note is gone and the pauses read the same as the clean file. The voice has not changed.
A buzz, 22 dB under
The same 60 Hz with 24 harmonics, the raspy edge a dimmer or a bad cable adds. Pitched, but thin and bright as well as low.
A buzz, after the fix
The low note is gone. The thin bright part above it is still there, because the fixer only takes the first five tones.
Rumble, 20 dB under
Pink noise below 120 Hz, like traffic through a wall or a desk picking up footsteps. Low, but with no pitch to it.
Rumble, after the fix
Identical to the recording. The check found no hum, so the fixer did nothing.
Public-domain LibriVox voice. The hum and the buzz are software sine tones, the rumble is filtered pink noise; nothing here came from a real ground loop, dimmer or desk. So the clean version really is what was there before.
| Case | The check | Pauses, 40 to 320 Hz | Pauses, 320 Hz to 3 kHz | Voice body |
|---|---|---|---|---|
| Clean reading | no hum, fine | -75 dBFS | -74.7 dBFS | -28.5 dBFS |
| Mains hum | -23.2 dB, moderate to no hum, fine | -44.6 to -75 | -63.4 to -74.8 | -28.4 to -28.5 |
| A buzz | -24 dB, moderate to no hum, fine | -45.3 to -70.4 | -54.7 to -55.2 | -28.5 to -28.5 |
| Rumble | no hum, fine to no hum, fine | -39.1 to -39.1 | -74.2 to -74.2 | -28.4 to -28.4 |
The mains hum is the case the fixer is for. The check reads it -23.2 dB under the voice, moderate; after the fix it finds no hum, the pauses drop 30.4 dB to the clean reading's level, and the body of the voice is unchanged to a tenth of a dB. That last number is the point of tracking tones a fraction of a hertz wide instead of cutting a band: a voice sits all around 120 and 180 Hz and loses nothing.
The buzz is the same tone with 24 harmonics, and it shows the fixer's edge. It takes out the first 5, so the low pauses drop 25.1 dB and the check now reads fine, but the band above 320 Hz is where it was, -55.2 dBFS against the clean reading's -74.7. You hear the difference as a thinner, brighter buzz that is still there. A fine reading after the fix means the mains tones are gone, not that the file is clean.
The rumble is a reminder that low is not the same as hum. The check reads it fine before and after and the fixer returns the file untouched, with -39.1 dBFS still in the pauses. That is a job for the noise fix or a high-pass filter, not this one.
What this does not prove: a real ground loop drifts in level and sometimes in pitch, which the tracking is built to follow but these steady tones do not test, and a buzz from a dimmer or a cheap supply can have far more energy up high than the five tones here. If you need to tell the three apart first, hiss, echo and hum explains how, and how we test has the pass marks behind the check.
How it works here
- 01
Pins down the hum
It looks near 50 or 60 Hz for a steady mains tone and the higher tones stacked on top, then estimates their pitch.
- 02
Tracks and subtracts it
It estimates the hum's slow changes, leaning on the pauses, then subtracts the mains tone and its first four harmonics.
- 03
Stays on your computer
Your file is never uploaded. The fix runs in this browser tab.
Questions
What causes hum in audio?
Mains electricity getting into the signal. The usual cause is a ground loop, when two pieces of gear are plugged into different sockets and connected by an audio cable. Unshielded cables running past power leads and phone chargers can do it too.
Is my audio uploaded anywhere?
No. The file is read and fixed inside this browser tab and never sent anywhere.
Does it matter if my hum is 50 Hz or 60 Hz?
No. fix.fm checks for both and finds the one in your file. 50 Hz is used in most of the world, 60 Hz in North America and parts of South America and Asia.
Will it affect a deep voice?
It can affect voice sounds that overlap a hum tone. Compare Before and After, and lower Amount if the voice loses body. The fix targets detected mains hum, not every kind of buzz.
How do I stop hum next time?
Plug all your audio gear into the same power strip, keep audio cables away from power leads, and try running a laptop on battery. A ground loop isolator fixes most stubborn cases.