Audio noise reducer

Reduce background noise in three steps

1. Choose an audio or video file, or press Try sample for a voice with hiss and a faint hum.
2. Set how much noise to remove, and switch on hum or rumble filters if you hear a low drone. Optionally enter a noise-only stretch in seconds.
3. Press Reduce noise, compare the before and after waveforms, listen, and download.

How the reduction works

The recording is cut into short overlapping frames and each frame is converted to a spectrum, which shows how much sound sits at each frequency. A noise profile is made from the quietest tenth of the frames, or from the seconds you give, and records how loud the background is at every frequency. For each frame the tool then compares the signal with that profile. Frequencies that are clearly louder than the noise, such as the vowels in speech, pass through. Frequencies that are close to the noise level are turned down by up to the reduction you choose. Gains are smoothed over time and neighbouring frequencies, which is how this classic spectral gating method limits the bubbling sound called musical noise.

What it can fix, and what it cannot

It works on noise that stays roughly the same: tape or microphone hiss, an air conditioner, a computer fan, a refrigerator, and the room tone of a quiet space. The hum option adds narrow notch filters at 50 or 60 Hz and the first three harmonics for mains hum, and the rumble option removes the low thump below 80 Hz from handling noise and traffic. It cannot remove a second person talking, a passing siren, music playing in the background, or echo, and it will not separate a voice from noise that sounds like the voice. Anything that claims otherwise needs a trained model; this does not use one.

Choosing the amount

Start at 12 dB of reduction and the default sensitivity. Higher values remove more noise but start to dull consonants and leave a watery or underwater quality, especially on voices recorded far from the microphone. If the result sounds processed, lower the reduction rather than the sensitivity. A recording with no moment of quiet gives the tool nothing to learn from, so enter a noise-only stretch, even half a second, or record a few seconds of room tone before you start next time.

Video, privacy and limits

For a video file, the picture is kept and the cleaned soundtrack replaces the original. A five-minute voice recording is processed in a few seconds on a modern laptop, but very long files take longer and use more memory on a phone. Noise reduction always changes the sound a little, so keep your original file, and judge the result with headphones before using it. All processing is local; nothing is uploaded.