Here’s how to install and use MP3Gain In Linux Mint / Ubuntu:
1. Issue the following command at the terminal –
sudo apt-get install easymp3gain-gtk
2. After the installation is complete, click on ‘Menu>Sound & Video>easyMP3Gain’ to start the application.
3. Now, to normalize volume of mp3 files, copy all the mp3 files (for which you need to normalize the volume) into a single folder. Click ‘File>Add folder…’ and then navigate and select the folder in which you have copied the mp3 files.
4. As soon as the mp3 tracks are added, they will be automatically analyzed for volume levels. Now click on ‘Modify Gain>Apply album gain’.
5. Sit back and relax while the volume levels of the mp3 files are normalized. You may get an message for access violation for some mp3 file, if they have been previously marked ‘read-only’; in that case click ‘OK’ to continue anyway.