How can I remove a constant hum from recorded audio?
Quick answer
First check whether the hum is steady and whether it appears throughout the recording or only in certain sections. In Audacity, Noise Reduction can target steady background sound: select a portion containing only the hum, create a noise profile, then apply reduction to the audio. Avoid including speech in the profile, use modest changes, and listen for damage; the tool can create metallic or watery artifacts, and it may not remove every hum.
The question, the details, the next step.
What should I check before trying to remove the hum?
Start by locating the hum and checking whether it stays similar across the recording. Listen to the beginning, middle, and end, including pauses where the sound is easier to hear. Note whether it is present throughout or only in particular sections, and whether speech overlaps it. These observations help you choose what to test; they do not identify the cause of the hum.
Keep an untouched copy of the recording. Then work on a duplicate or a separate project version so you can compare the edited result with the original. Record your observations in a small note:
- Where the hum is audible: [timestamps or sections]
- Whether a section contains only hum: [yes / no / unsure]
- What matters most to preserve: [speech, music, other sound]
- What you want to compare: [original / test edit]
If there is no section with hum alone, do not assume a speech-containing passage is a suitable noise sample.
How do I use Audacity’s Noise Reduction for a steady hum?
Audacity’s Noise Reduction can target steady background sound, including hum. The documented workflow is to profile a segment that contains only the noise, then apply reduction to the selected audio. Be careful not to include wanted speech in the profile: speech can be treated as noise too. [S1]
A cautious workflow is:
- Find a short passage where the hum is audible and wanted sound is absent.
- Select that passage and create the noise profile using Noise Reduction.
- Select the audio you want to treat and apply the effect with restrained settings.
- Listen to the result, then compare it with the unprocessed version.
The manual warns that strong reduction can make audio sound metallic or watery. Its “Noise only” output is a useful check: listen to it to see whether wanted signal, such as speech, is being removed. If the noise-only check contains recognizable speech, back off or reconsider the profile rather than pushing the reduction further. [S1]
What if the hum continues under all the speech, so there is no clean sample?
Do not use a passage with speech as though it were hum alone. The Audacity manual specifically cautions that wanted speech in the profile can also be treated as noise. [S1] If no clean sample exists, the documented approach may not fit your recording as-is. You can still make a small test on a duplicate, listen to the “Noise only” output, and keep the edit only if the speech remains acceptable.
Work on a short representative section first, then compare it with the same section in the original. Check quiet speech, louder speech, and pauses; a result that reduces hum in a pause may still damage wanted sound elsewhere. If you cannot get an acceptable trade-off, keep the original and consider asking an audio editor to review a sample. This source explains Noise Reduction for steady noise, but it does not establish that every hum can be removed or document a dedicated notch-filter workflow. [S1]
How should I decide whether the finished edit is good enough?
Judge the edit against the original, not against an expectation that the hum must disappear completely. Listen at a comfortable level to the same sections in both versions. Check whether words remain clear, whether the voice sounds natural, and whether reduction has introduced metallic or watery artifacts. Use Noise only as an additional check for wanted speech being removed. [S1]
Keep a brief review note so you can reproduce or undo your choice:
Test section: [timestamp] | Profile: [hum-only / not available] | Change: [setting or description] | Speech: [acceptable / affected] | Artifacts: [none noticed / describe] | Decision: [keep / revise / revert]
This is a listening workflow, not a guarantee of removal. The cited guidance does not say how a particular recording will respond, nor does it establish that all types or levels of hum can be eliminated. If every test harms the speech, reverting is a reasonable result.
A practical checklist
Save an untouched copy before editing.
Listen across the recording and note where the hum occurs.
Use only a hum-only segment to create a Noise Reduction profile.
Test restrained reduction on a duplicate before treating the full selection.
Check Noise only for speech or other wanted sound being removed.
Compare edited and original passages; revert if speech sounds damaged.
A few more useful answers
Can Noise Reduction guarantee that all hum will disappear?
No. The Audacity manual describes a method for targeting steady background sound, but does not establish that every hum can be removed. [S1]
Why should I listen to the “Noise only” output?
It helps check whether wanted audio, such as speech, is being treated as noise. If you hear wanted content, reconsider the profile or reduce the processing. [S1]
What if the edit sounds metallic or watery?
Strong reduction can produce those artifacts, according to the Audacity manual. Compare with the original and try less reduction or revert if the speech is affected. [S1]
Sources
References used for this guide.
- [S1] Noise Reduction — Audacity Manual audacityteam.org · Checked