Know which noise you have
Before you remove background noise from audio, work out what kind of noise it is, because different noise needs different fixes. The most common kind is steady noise: hiss from a microphone preamp, the whoosh of an air conditioner, a laptop fan, a fridge humming in the next room. It sounds the same from one second to the next, and it is the easiest kind to remove.
Electrical hum is its own category. It is a low, steady tone at the frequency of the mains power, 60 Hz in North America and 50 Hz in Europe, Australia, and most of Asia and Africa, plus a stack of higher tones above it. It usually comes from a ground loop, a cheap cable, or a microphone cable running alongside a power cord.
The third kind is changing noise: passing traffic, people talking, a dog barking, music in another room, keyboard clicks. Because it never sounds the same twice, it is much harder to remove without damaging the voice. And one common problem is not noise at all. A voice recorded in a bare room with hard walls picks up echo, and noise reduction does not remove echo.
How noise reduction works
Classic noise reducers, like the Noise Reduction effect in Audacity, use a technique called spectral noise reduction. First the software needs a noise print: a short stretch of the recording where you hear only the background, like the pause before someone starts talking. It measures how loud the noise is at every frequency. Then it works through the entire file and turns down each frequency whenever the sound there is no louder than the noise print.
Where your voice is present, it rises well above the noise and passes through. In the gaps between words, the noise gets pulled down. Done gently, the result sounds like the same recording made in a quieter room.
Remove background noise for free, step by step
We built a free Noise Reducer that works this way. It runs in the browser, nothing uploaded, we never see the file, which matters for recordings that are private by nature: interviews, voice memos, meetings, and vocal demos.
Drop in your recording and leave strength on Medium to start. If you hear an electrical hum, set hum removal to your mains frequency. Press Reduce noise, and the tool finds the quietest moment in the file, learns the noise from it, and cleans the whole recording, including the part before that quiet moment. Listen to the preview on headphones, then download an MP3 or a WAV.
If the recording has no quiet gap at all, the tool falls back to an automatic mode that estimates the noise as it goes. That still helps, but more gently, which is one more reason to leave a second or two of silence at the start of every recording.
Avoid the underwater sound
Push noise reduction too hard and a new problem appears: a watery, swirling, underwater quality, sometimes with faint chirps in the background. Audio engineers call those chirps musical noise. It happens when the noise is loud compared to the voice, so the software cannot cleanly separate the two and starts removing parts of the voice along with the noise.
The fix is restraint. Try Gentle first on noise you can barely hear, and save Strong for when the noise is clearly the bigger problem. A little background noise usually sounds more natural than an overprocessed voice, and listeners forgive a quiet hiss far more readily than a robotic one.
Order matters too. Remove noise before you compress a recording or raise its volume, because both of those make the noise louder along with everything else. Once the recording is clean, level it with the Volume Booster, which can normalize speech to a consistent loudness without clipping.
What noise reduction cannot fix
Noise reducers are built for steady sounds, so they struggle with anything that changes: background conversations, sirens, barking, wind gusts, and music. Music behind a voice is the hardest case, because it overlaps the voice in frequency and never repeats one pattern. That job needs source separation, which uses AI to split a recording into parts like vocals and instruments. Our desktop app, Xport Studio, does that offline on your own computer.
Heavy room echo is also out of reach. Tools for reducing reverb exist, but they are a different kind of process, and the best cure is still recording in a softer space.
Record cleaner next time
The best noise reduction happens before you press record. Get closer to the microphone: halving the distance makes your voice about 6 dB louder while the room stays exactly as loud, so every bit of background noise matters less. Switch off fans, air conditioning, and fridges if you can. Record in a room with soft furnishings, like a bedroom with curtains, a rug, and a bed, instead of a kitchen or a bathroom.
Finally, record a few seconds of silence at the start, without moving. That clean stretch of room tone is exactly what a noise reducer needs to learn from, and it costs you nothing.