Does this sound app exist?

[tomhorsley at adelphia.net]

Does any kind of "dynamic mixer" exist for alsa sound? I want something that will
monitor the sound level and increase the volume when it is too low and decrease
it when it is too high automagically. A lot of media player applications have such
a feature, but it only works in that player. I'd like to be able to enable the same
effect on a global level, regardless of where the sound is coming from. (Yes, I
know it will destroy the purity of beautiful audio tracks that are intended to have
a wide dynamic range - I don't care - I'll disable it when I'm feeling artistic, but
for normal use I want to be able to hear stuff without being blasted out of
my chair when something loud comes along :-).