By Harpal Singh · · 6 min read
The recording is good. The explanation is clear, the demo works, and under all of it there is a hum. Or a fan. Or the traffic you did not notice until you played it back. The question is whether you can take that out without re-recording. Audio background noise removal is a repair job with a hard limit, and where that limit sits depends entirely on what kind of noise it is. To eliminate background noise in a video completely you would have to remove it at the source, which is why most of this guide is about reducing it.
Which background noise can be removed?
Noise falls into two groups, and they behave very differently.
Steady noise is constant and does not change with what you say: a fan, an air conditioner, the hum from a power supply, hiss from a cheap microphone, a computer's own fans. Because it is predictable, a filter can reduce it without touching your voice.
Unsteady noise changes while you talk: a conversation in the next room, a dog, a siren, music, keyboard clatter, a notification chime. It overlaps the same frequencies as your voice, and once it is mixed into one track a simple filter cannot tell which is which.
Almost every "how do I remove background noise from a video" problem is one of those two, and the answer to the first is "yes, mostly" and the second is "reduce it, not remove it".
What does a high-pass filter do?
A high-pass filter removes the low rumble below a chosen frequency and leaves everything above it. Voices sit well above the rumble of a desk knock, an air conditioner or a passing lorry, so cutting the bottom end makes a recording sound cleaner and more present at almost no cost to the voice. It is the first thing to try, and it is safe because it rarely damages anything.
What does a noise gate do?
A noise gate turns the audio down when you are not speaking. While you talk the gate is open and everything passes; in the gaps between words it closes, so the fan or the hiss disappears from the pauses. A soft gate eases in and out so it does not chop the ends of words.
Its limit follows directly: it can only hide noise in the gaps. While you are speaking, the noise is still underneath your voice, just masked by it. For steady noise that is usually enough, because a loud voice hides it. For a loud environment it is not.
How do you reduce noise in a screen recording with ReScreen?
ReScreen keeps your microphone and the system audio as separate tracks, so you clean up your voice without touching the sound of the app.
- Open the recording in the editor and find the audio controls for the microphone.
- Switch on Reduce background noise. It applies a high-pass filter and a soft noise gate to the microphone track, which quiets steady room noise between words.
- Switch on Level voice volume if your volume wanders.
- Set Voice enhancement to Light, or to Strong for a firmer filter and gate that also holds the loudest peaks down.
- Play it back at the level you will export, then export.
The cleanup applies to the microphone track only, and it is applied when the project plays and exports, so the captured audio is never written over and you can change your mind later. There is no threshold slider: how firmly the gate closes is set by the Light or Strong choice. Audio cleanup lists each control, and how to fix bad audio in screen recordings walks through the common cases.
What can't it do?
Be clear about the limits, because they are the difference between a fix and a disappointment. ReScreen's noise reduction is not neural speech isolation. It does not pull your voice out of a recording with another conversation in it, and it does not cancel the echo of your own speakers, so wear headphones when you record microphone and system sound at the same time. If a take is ruined by unsteady noise, the repair is to record the section again in a quieter room.
Do video editors have noise reduction?
Yes. General video editors such as iMovie and Final Cut Pro include noise reduction controls for the audio of a clip, and they are a sensible route if you already edit there. They work on a clip's soundtrack, so everything is one mix: system sound and voice are already combined by the time they reach the editor. That is one reason to keep tracks separate at recording time. Separate audio tracks in a screen recording explains the difference.
What about online noise-removal tools?
Many tools that remove noise from video, especially the ones that advertise themselves as free and online, work by uploading the file to a server. For a recording of your own voice that may be acceptable. For a screen recording it means the whole screen goes with it: customer data, internal dashboards, an inbox you forgot was open. Check what a tool does with the upload before you use it for anything sensitive. A local tool avoids the question entirely, which is the argument in a private, offline screen recorder for Mac.
How do you edit out background noise in a video?
To edit out background noise in a video, start by finding which track the noise is on, because that decides what is possible, and remove certain sounds one at a time rather than all at once. To clean up the sound in a video, work in this order. A chime or a notification from the app sits on the system audio track, so lower or fade that track at that moment and your voice is untouched. A cough, a door or a passing car on the microphone track can be cut out or turned down for that second. To remove ambient noise from a video, a filter is the right tool for the steady kind under the whole take, sometimes written as bg noise: reduce it. To get rid of background noise in audio that has been flattened into one track, you can reduce it but never separate it, which is why the honest advice for a loud take is to record it again.
Can you remove background noise from a video online for free?
Yes, with tools that upload the file, and that is the cost. A free online tool to remove noise from a video is fine for a clip you would happily publish. For anything else, such as a screen recording, a local route is better: a general video editor's noise reduction, or a recorder that cleans the voice track before export.
How do you avoid the problem next time?
Prevention beats repair, and it is quick.
- Get closer to the microphone. Distance is the biggest lever you have.
- Stop the source. Turn off the fan, close the window or move to another room before recording rather than after.
- Check the room first. Record five seconds of silence and listen on headphones.
- Use a headset or an external microphone when the built-in one picks up your keyboard.
- Record the voice and the app separately. A fixable voice track beside an untouched app track is a better position than one flattened mix.
If audio is the whole job, how to record audio on a Mac covers the built-in tools. If the recording is of your screen, download ReScreen for macOS and see what the cleanup controls do on your own take.
Filed under
