hldj.org

Read on the front page that a program that will convert the mp3's to wav properly is up and coming, and I thought that if you are going to do that, you might as well do something that sets the song at a tolerable volume level, because if HLDJ automatically converts it to wav people are going to think it's fine as is and immediately go in game, then start blasting that stuff.

Yep, the thought occurred to me and it certainly is possible. In the meantime until I revamp the GUI/settings format, I'll probably just implement a vanilla converter (clipping volume at the highest peak).
Other things that may be adjustable are pitch, filtering, and some basic effects, though I'm still deciding as to where to draw the line between built-in/lightweight vs. full-fledge.

Right now I'm using MAD for decoding, but it's also possible if I get time to figure out FFmpeg I may switch to that as it supports many more features and effects.