Each album has a different volume, and if you want to play them all together at a low background level, you better put them all into a directory and normalize them. This is done with 'normalize-audio' which can be directly installed by your usual update process.
Just go into that massive directory and type 'normalize-audio *'. It's magnificent!
I'm going to try this for vlc.
Are you constantly adjusting the volume in movies? Music, explosions, gunshots, etc. too loud? Conversations too quiet? If this is your problem, read on. I am combining information found in multiple threads for convenience.
Navigate to Tools>Preferences. Select Audio. Check the "Normalize volume to:" box and set the value to 1.6
Now switch to Advanced view by selecting "All" in the "Show Settings" box at the bottom left
Expand "Audio" and highlight "Filters". Check the "Volume Normalizer" box. You should see "normvol" added to the text box at the bottom
Expand "Filters" and highlight "Volume Normalizer". Set "Number of audio buffers" to 10 and "Maximal volume level" to 1.6
Hit the "Save" button at the bottom
Restart VLC, as settings are not applied until restart. As I did this in increments, you may have to apply one step, save, and restart VLC between for menu options to be present. I haven't tested applying all settings at once, but I believe you can do this all at once.
Double-check all settings are correct after VLC is restarted.
Whoops. The vlc method is just good for a single track, like if you don't want the house to rumble during the battle scenes, but you want the speech up to understand the English accents.