So I copied the section below into /etc/asound.conf:
These plugins need to be installed though: apt-get install swh-pluginspcm.ladcomp { type plug slave.pcm "ladcomp_compressor"; } pcm.ladcomp_compressor { type ladspa slave.pcm "ladcomp_limiter"; path "/usr/lib/ladspa"; plugins [ { label dysonCompress input { #peak limit, release time, fast ratio, ratio controls [0 1 0.5 0.99] } } ] } pcm.ladcomp_limiter { type ladspa slave.pcm "plughw:0,0"; path "/usr/lib/ladspa"; plugins [ { label fastLookaheadLimiter input { #InputGain(Db) -20 -> +20 ; Limit (db) -20 -> 0 ; Release time (s) 0.01 -> 2 controls [ 20 0 0.8 ] } } ] }
Now the tricky part, getting your programs to actually use this stuff. You have to tell your program to use the ladcomp alsa device. Mplayer and Xine are pretty easy, you can just type it in a box in the gui. However, Gnome's Movie Player (Totem) is a bit trickier. Google to the rescue: http://www.mail-archive.com/gnome-list@gnome.org/msg02589.html
Basically open Configuration Editor and change
system -> gstreamer -> 0.10 -> default) changing the key "musicaudiosink" from "alsasink" to "alsasink device=ladcomp"
All my movies seem to be nearly the same volume now. I setup xine to use it as well, and played a DVD and it seemed to be just a bit louder than movie files, so I'll have to look more into exactly what this filter is doing, maybe it is not reducing loud volume, but just cranking up low volume?