Dynamic range expansion, opposite of compression

Audacity Help Forum GNU/Linux
1

I use Audacity 2.3.3 on Linux Mint 20 Cinnamon.

I am looking for a means of making loud passages louder and low passages lower. I recorded a piece of audio from a video where the audio is overly compressed. I want to try to undo this. For that, I need a range expander.

I saw a thread from 2008 asking for a range expander, but the link to a compressor plug-in that can use negative numbers to achieve expansion was blocked.

Is there such a solution for Linux Audacity?

Thanks!

2

I don’t know but you might want to look for a 3rd-party VST plug-in.

The Clip Fix effect can push-up peaks and the Noise Gate will lower quieter parts but they probably won’t do what you want.

I recorded a piece of audio from a video where the audio is overly compressed. I want to try to undo this.

I’ve tried that with GoldWave (for Windows*) a couple of times and although it made the waveform look better it didn’t really improve the sound… Certain kinds of compression & limiting can’t be properly reversed and if it’s highly-compressed there’s not much to work with…


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  • There is an older version of GoldWave that’s supposed to run on Linux/Wine. It’s not free but there is a fully-functional free trial. If you do try it, the compressor/expander terminology is fouled-up but there are presets for “boost loud parts” and “reduce quiet parts”. GoldWave also has a “dynamics” effect that can compress or expand sample-by-sample without any attack or release time.
3

I think that’s Chris’s compressor plugin …
https ://manual.audacityteam.org/man/chris_s_dynamic_compressor.html
It’s specifically for Audacity so should work on Linux.

4

I recorded a piece of audio from a video where the audio is overly compressed.

I wonder if you have a Dolby® track. It’s hard to make a music track so compressed that it’s hard to listen to using regular audio and music tools, but it’s a snap in Dolby. Dolby tracks are surgically compressed and dynamically limited at the beginning and you need to use a Dolby player at the other end to undo it and restore the show to normal.

If you listen to a Dolby track without the decoder, the music will sound weird with obvious volume pumping and noise problems through the performance. If you have a Dolby-C track, the music can be almost unlistenable.

I don’t know any way out of that. Dolby is patented and protected and copyrighted as one of the few music systems that, when done properly, you can’t tell it’s working. I think Digital Broadcast in the US uses one of the Dolby processes.

Did you get a split track video where the sound went through a different process than the picture?

It’s also possible you’re listening to MP3 compression and mistaking it for loudness processing. MP3’s full family name is MPEG-1, Layer 3. It’s part of a video format.

Koz

5

Thanks, Trebor. I did add the advanced Compress. With it, I can record myself and take out background noise. It uses negative numbers to decompresses audio, but I haven’t worked enough with it yet.

After looking it up, I have a better understanding of companding. Companding involves the broadcaster compressing and the recipient expanding to restore the original dynamic range.

I think Chris’ Advanced Compress Dynamics would likely allow me to expand the dynamic range if I knew what the original compression involved.

6

if I knew what the original compression involved.

Ding!

That’s the problem with free-form de-compressing. Unless you were a party to the process at the beginning, like Dolby, you have no idea what the original software did, and no good way to find out.

You can create some really cartoony results by just guessing at it. Worse yet, some jobs such as broadcast treat overall loudness and expressive peaks differently. You have to know about and take both corrections out to get back to the original.

Kozc

7

It’s a YouTube video from ABC News, and perhaps it does have Dolby® involved. I am not familiar with Dolby®, except back in the tape days when hiss was the enemy. I’ve been listening to the live news broadcasts from NBC or ABC on YouTube.

Dolby® boosted the high notes while recording and then reduced the high notes and the hiss with playback. The alternative to Dolby® was to reduce the treble.

I think I hear so much compression because a guest on the show is at home in front of his computer with less-than-desirable acoustics. Add broadcast compression to that!

8

a guest on the show is at home in front of his computer with less-than-desirable acoustics.

Oh, it’s far worse than that. Were they wearing headphones? If not, then Zoom was also gating the host’s voice on the guest’s microphone so it doesn’t create a feedback condition.

You can do everybody a really big favor on a conference call by setting up in a quiet room and wear headphones or earbuds. Simple tricks.

Koz