Remove hum from audio: 50 and 60 Hz, and the buzz above it.
Drop a recording or a video with a mains hum in it, the low drone from a ground loop, a guitar amp, a cheap power supply or a light dimmer. The page finds the hum, measures its exact frequency, follows it through the file and cuts it out with its harmonics, in notches so narrow that the voice or music between them is left as it was. Nothing is uploaded.
drop the recording or video with the hum
MP3, WAV, M4A, FLAC, voice memos, or an MP4, MOV or WebM video. Several at once is fine.
| Hum found | — |
|---|---|
| Its frequency | — |
| Removed | — |
At a glance
| Finds | 50 or 60 Hz mains hum by itself, its frequency measured to a hundredth of a hertz |
|---|---|
| Follows | The mains frequency as it wanders through the file, second by second |
| Removes | The hum and its harmonics: the first four, everything up to 1 kHz, or up to 4 kHz for buzz |
| Measured | Hum 42 dB down under speech; the speech level moved 0.13 dB |
| Leaves | The timing and length exactly as they were (zero-phase filtering); a video's picture copied untouched |
| Out | WAV or FLAC at the source's own rate and depth, float WAV, MP3 or M4A |
| Uploads your files | No |
What hum is, and why it is hard to remove
Mains electricity alternates 50 times a second in Europe, the UK, most of Asia, Africa and Australia, and 60 times a second in North America, much of South America, Taiwan, Korea and the west of Japan. When it leaks into a recording, through a ground loop between a laptop on its charger and a mixer, an unbalanced guitar cable, a lavalier receiver beside a power brick, or a dimmer on the same circuit, it arrives as a low drone at that frequency. Above it sit harmonics at two, three, four times the frequency and up. A transformer gives a soft hum, mostly the fundamental and the second harmonic; a rectifier or a dimmer gives a harsh buzz, where the odd harmonics reach well into the kilohertz.
A broad cut at 60 Hz takes the bass of a voice with it and leaves the buzz above. What works is a separate narrow notch on every harmonic, and that only works if each notch sits exactly on its harmonic. The grid is never exactly on 50.00 or 60.00 Hz: it wanders by a few hundredths of a hertz as demand changes, and an old tape or a recording made off speed moves it further. A 0.03 Hz error is 0.24 Hz at the 8th harmonic, which is enough to slip out of a notch narrow enough to leave the voice alone.
How this hum remover works
First it listens. A low-passed copy of the first minute is searched from 47 to 53 Hz and from 57 to 63 Hz for the frequency whose harmonics carry the most energy, then refined to a hundredth of a hertz. It is called hum only when at least two harmonics stand 10 dB above the sound a few hertz either side, so a voice or a bass line is not mistaken for it. Clean speech, in the check that comes with this page, does not trigger it. Then it follows the hum: every second, a four-second window is searched again within 0.15 Hz of that frequency, so the notches move with the mains as it drifts. Then each harmonic gets its own notch, under 2 Hz wide, run forwards and then backwards over the file. That cancels any phase shift, so nothing is delayed or smeared, and it doubles the depth. At each end the hum itself is carried on past the file for the notches to settle on, so the first and last seconds are cleaned as well as the middle.
The check behind this page plays a minute of speech over hum at -30 dBFS with eight harmonics, set at 59.97 and 50.04 Hz and wandering 0.03 Hz either way, as the grid does. It finds the right mains each time and measures the frequency within 0.01 Hz. The hum comes out 42 dB quieter, and the speech level changes by 0.13 dB.
Which setting to use
Leave Mains on "Find it" unless the page says it found nothing and you can still hear a hum; then choosing your country's frequency removes it anyway. "Hum", every harmonic up to 1 kHz, is right for most recordings. "Light" takes only the first four harmonics, for music where you want to touch as little as possible. "Buzz" goes to 4 kHz, for the angry, edgy sound of a dimmer or a single-coil guitar pickup near a monitor. For speech it costs nothing audible; on sustained music the more notches, the more chance one lands on a note that happens to sit on a harmonic.
What it doesn't do
It removes hum, not other noise. Hiss, fans, air conditioning, traffic and room tone have no fixed pitch, and the noise reduction tool deals with those. A hum loud enough to clip the recording leaves distortion that no filter can undo. The tools sold for this, iZotope RX's De-hum, Adobe Audition's DeHummer and Waves X-Hum, do the same job and add adaptive learning that helps on difficult buzz. Audacity has a Notch Filter but no automatic tracking. If you can, fix it at the source before the next session: a ground-lift or a DI box on the guitar, the laptop on battery, balanced XLR cables, and audio cables crossing power cables at right angles.
FAQ
How do I remove hum from audio for free?
Drop the file above and press Remove the hum. The page finds whether it is 50 or 60 Hz, measures the exact frequency and removes it with its harmonics. Nothing is uploaded and there is no account.
Is my hum 50 Hz or 60 Hz?
It depends on where it was recorded: 60 Hz in North America and parts of South America and Asia, 50 Hz in Europe, the UK, Africa, most of Asia and Australia. You do not need to know; the page measures it.
Will it change the sound of the voice?
Very little. Each notch is under 2 Hz wide, so the voice between the harmonics is left alone. In the check, a minute of speech changed level by 0.13 dB while the hum came down 42 dB.
Can it remove hum from a video?
Yes. Drop an MP4, MOV or WebM. The sound is cleaned and put back beside the original picture, which is copied without being re-encoded, so the video stays exactly as sharp and in sync.
It says no hum was found, but I can hear it. Why?
The automatic finder only calls it hum when its harmonics stand clearly above the rest of the sound. Choose 50 or 60 Hz under Mains and it will be removed anyway. If it is a hiss or a whine rather than a low drone, it is not mains hum; try the noise reduction tool.
What causes the hum in my recording?
Most often a ground loop: two pieces of gear plugged into different sockets and joined by an audio cable, such as a laptop on its charger feeding a mixer or an amp. Single-coil guitar pickups, light dimmers and unshielded cables near power supplies are the other usual causes.
What is the difference between hum and buzz?
Hum is mostly the mains frequency and its first few harmonics, a soft low drone. Buzz has strong harmonics up into the kilohertz and sounds harsh. Choose "Buzz" for that: it removes harmonics up to 4 kHz.