How to remove audio noise from MKV videos
November 18, 2020 10:44 AM   Subscribe

I have some MKV videos that I need to transcribe. They have a sort of humming background noise which is presumably made by some nearby machines. They DO have some otherwise silent portions of video (where the background noise can be sampled). What's the best way to remove the background noise. I'd like to open the file, click a few buttons/choose a few options and then save-as. I do not want to become an audio engineer or pull the audio out of the video and then re-insert it or whatever.

Free preferred. Not-too-expensive acceptable, especially if I can do a free trial (Even if I can't save -- just to hear that it works on my files).

These are confidential videos, so an online solution is not acceptable.
posted by If only I had a penguin... to Computers & Internet (10 answers total) 1 user marked this as a favorite
Without extracting the audio I would try this in VLC (free download if you don't have it). Note that these changes will be applied to the whole file, you would be able to be more subtle in just filtering the noisy sections if you were to extract and edit audio and then re-import - but yes - that is a lot more work.

In VLC I'd try:

Go to "View" in menu.

Click on Show Audio Effects Button.

This brings up a little button in the lower right corner with a stylised equaliser icon.

Click on it and play back a section with the unwanted noise. Try pulling down frequency bands (you might need to reduce multiple bands) to see if this reduces the noise without impacting other sounds you want to keep.

Good luck!
posted by multivalent at 11:05 AM on November 18

Sorry to threads it. Having tried VLC, I just want to clarify two points.

1. I was hoping for something that would let me sample the noise from the file and then remove that sound. (Yes, from the whole file. All the files have the same hum from the same source. Same mic positioning. Same room. Same everything).

2. I need to be able to save a noise-free version of the file. Something that just adjusts the playback won't work.
posted by If only I had a penguin... at 11:18 AM on November 18 [1 favorite]

Ok - in that case you can try and use Audacity also free (it's an audio-centred software) but you can import video files direct if you also install support for FFmpeg library.

Rather than type out the steps read this guide (second approach listed on the page). This way allows you to get a "noise profile" from a section which contains as little other audio information as possible apart from the offending source and compensates accordingly.

At this point I think you'd have to export the new audio as an audio file type and then you could re-join it with the video component in VLC.

It's a fairly complex requirement, and I'm not aware of a simpler way to do it.
posted by multivalent at 11:32 AM on November 18 [2 favorites]

remove audio noise ffmpeg - Google Search might have something. Second Audacity has a smarter "here's the noise", "now remove that from the file" feature and you'll end up extracting the audio from the MKV, processing it, then putting it back in. I'm not sure about Audacity's automation capabilities, but ffmpeg would be easy to batch the extraction/insertion of the audio bit.

I know I did this once with ffmpeg and a conference video but don't remember exactly how, probably Googled it.
posted by zengargoyle at 2:09 PM on November 18

I would try Reaper. You can use a trial version for free without any limitations on the functionality, or pay the reasonable license fee if you like it ($60).

It does have video editing capabilities, so I assume you'd be able to import and edit the audio, but my experience with it is primarily audio-only so I'm not 100% sure if there would be any hitches to importing your file.

You can use the built-in plugin ReaFir to remove the noise and it should be really easy:

1) Insert the file into a new track in your project
2) Add ReaFir as a plugin on your track
3) Select "Subtract" as the mode and "Automatically build noise profile"
4) Go to one of the "silent" portions of audio and hit play, then stop before anything you want to keep comes in.
5) That's it! The plugin will have made a little wave form from listening that it then subtracts from all the audio on the track.

Tutorial here.
posted by music for skeletons at 2:22 PM on November 18 [2 favorites]

P.S. Also, a heads up that Audacity is a destructive audio editor, so if you do something to your files and save and then change your mind, there's no going back. Make sure you back your files up if you end up using that. Reaper is not destructive.
posted by music for skeletons at 2:24 PM on November 18

If you have a bit of a budget, the Waves X-Noise plugin is amazing for this.
posted by transitional procedures at 3:54 PM on November 18

Soundsoap is a product that exists exactly for this use case. It is very effective but it is not free, though there are some free trial options that may work for you.
posted by SaltySalticid at 6:25 PM on November 18

I'm not an expert on removing noise from audio, but if you're able to do so on an audio file (MP3, AAC, etc.) vs. a video file, I'd recommend the GUI version of MKVToolNix.

An MKV is a container file that includes the video, the audio, any any other supplemental data. MKVToolNix is a suite of tools that will let you pick out the audio file to edit separately as you wish. When you're ready you can add it back to the file (you can even include both audio tracks in the same file if you want to preserve the original).

It's an open-source project and built for the command line so it can be a bit wonky, but the GUI interface is pretty easy to use once you wrap your head around it.
posted by owls at 11:43 AM on November 19 [1 favorite]

Building a profile can have other undesirable effects - most of the time humming can be taken out by throwing a high pass filter on the whole audio track. This should be painless in Reaper.
posted by aspersioncast at 5:21 PM on November 19

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