Just to elaborate: this is called dynamic range compression ... not to be confused with audio data compression. The former is what makes the MP3's in the first place -- but the latter actually limits the output audio and prevents it from "being too loud."

This can be done in Perl, i am quite sure ... but the problem is how does one attach a "virtual filter" to the output of the program playing their MP3 files? This is why so many people just solve the problem with hardware instead.

UPDATE: drats -- I had it right the first time, sasdrtx. :) I used to be a janitor but I don't do that no more. Someone else can fix it. ;)

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)