You are gonna hafta read up a bit here if you want the answers. Start with the FAQ and maybe a search for dynamic compression
As for the .dll, it is the equivalent of an plugin for the audio player/recorder/bestfriend foobar2000. www.foobar2000.org
If you use winamp, there are dynamic compression plugins available, but none that I have tried really lived up to the hype. There is a new multiband dynamics plugin available
http://www.hydrogenaudio.org/forums/index....33&hl=multibandthat is supposed to be pretty good.