Hum, hiss and fan noise are the three steady sounds that creep into almost every home and office recording. They don't need the same fix. Hiss and fan noise are broad, steady sounds that a speech noise remover reduces well. Electrical hum is a fixed tone, and the reliable cures are fixing its source or a hum filter in an audio editor.
This guide covers where each comes from, what to do about each in a recording you already have, and how to stop it next time.
Know which one you have
Listen to a few seconds with nobody talking, on headphones.
| Sound | What it sounds like | Usual cause |
|---|---|---|
| Hum | A low, steady tone, sometimes with a buzz on top | Mains electricity: ground loops, chargers, lighting, cheap cables |
| Hiss | A soft "shhh", strongest in the high frequencies | Microphone and preamp self-noise, gain turned up too far |
| Fan / AC | A broad whoosh or drone, sometimes with a slow wobble | Laptops, desk fans, air conditioning, heaters, extractor fans |
Many recordings have more than one. A laptop recording in a warm room might have a fan, a little hiss from a built-in microphone and a faint hum from the charger.
Where they come from
Hum
Electrical hum sits at the frequency of the mains supply, 50 Hz or 60 Hz depending on the country, plus its harmonics, which is why it can sound like a buzz rather than a pure tone. Common sources are a ground loop (two devices plugged into different sockets and connected by an audio cable), a laptop charger, dimmer switches and fluorescent or cheap LED lighting, and unbalanced cables running alongside power cables.
Hiss
Every microphone and preamp adds a little noise of its own. You hear it when the gain is turned up a long way to make up for a quiet voice or a distant microphone. Budget USB microphones and built-in laptop microphones tend to hiss more.
Fan and air conditioning
Moving air and spinning motors make a broadband noise that covers much of the same range as the voice. It's steady, but loud fans can be surprisingly strong in a recording because the microphone hears everything the room does.
Fixing a recording you already have
Hiss and fan noise: the quick way
For spoken recordings, a speech-focused noise remover reduces hiss and fan or air-conditioning noise in one pass, because it keeps the voice and lowers the steady sound around it rather than targeting one frequency.
- Drop the file into the noise remover for audio (WAV, MP3, M4A/AAC, OGG/Opus and FLAC work) or, for a video, the video noise remover.
- Turn on Voice clarity if the voice sounds boomy or boxy; it trims low rumble and adds presence. It is a tone control for the voice, not a hum filter.
- Preview the original and cleaned versions at the same moment, focusing on the pauses and on soft words.
- Download, in the same format or as WAV, MP3 or M4A.
Our speech AI is not a noise gate, so the steady background doesn't switch on and off between sentences; it is removed under the words as well.
Hum: fix the source, then filter it
Our tool is built for hiss and broadband noise such as fans and air conditioning; it is not a hum remover, so treat electrical hum on its own.
- Re-record if you can. If the take can be repeated, fix the cause first (see below). A hum that was never recorded beats any filter.
- Otherwise, filter it in an editor. Use a notch filter (a very narrow cut) at 50 or 60 Hz, plus further notches at its multiples if the buzz remains. Many editors have a dedicated hum-removal effect that finds the frequency and sets the notches for you.
- Then clean the rest. If the filtered file still has hiss or fan noise, run it through the noise remover afterwards.
Hiss and fan noise by hand
If you prefer to work in an editor:
- Hiss: classic noise reduction with a noise profile taken from a pause works fairly well because hiss is steady. Use the gentlest setting that works; heavy settings make speech watery. A low-pass filter can also tame hiss, but it dulls consonants such as "s" and "t".
- Fan noise: noise reduction from a profile again, gently. Because fan noise overlaps the voice, manual reduction usually leaves a trade-off between remaining noise and a hollow-sounding voice.
Honest limits
- If the fan is right next to the microphone or louder than the voice, cleaning will leave some trace or affect the voice slightly.
- A hum filter cuts narrow bands. A strong buzz with many harmonics needs several notches, and too many can thin the voice; fixing the source is always cleaner.
- Hiss from a microphone with the gain turned up very far often comes with a thin, distant voice. Cleaning removes the hiss but can't make the voice closer.
- Noise tools don't remove echo; that's a property of the room, not noise on top of the voice.
Stopping them next time
Hum
- Plug the computer, interface and any powered speakers into the same power strip.
- Unplug the laptop charger while recording, if the battery allows.
- Keep audio cables away from power cables, and replace any that crackle when moved.
- Turn off dimmers and suspect lights and see whether the hum changes.
Hiss
- Move the microphone closer so you can turn the gain down. This is the single biggest fix.
- Use the microphone's own gain control rather than boosting a quiet recording in software later.
- Consider a dynamic microphone for untreated rooms; they need the voice close, which keeps the room and the hiss low.
Fan and AC
- Switch them off for the take, or set them to the quietest speed.
- Point the microphone away from the noise source; most microphones hear less from behind.
- Close heavy apps so the laptop fan stays quiet, or put the laptop on a hard surface further from the microphone.
A quick reference
- Hum = electrical, low tone. Fix the wiring; a notch or hum-removal filter in your editor after.
- Hiss = gain too high or a noisy microphone. Get closer; noise reduction after.
- Fan = moving air. Switch it off; a speech noise remover handles it best after.
For the bigger picture on recording conditions, see how to record clean audio at home. If the recording is a video call, why your Zoom recording sounds bad covers the extra problems call software adds.