Mp3/ midi volume changer

I made a few mp3 and midi files from finale, and the volume is just a notch too soft. Any softwares (preferably free) to change the volume of 'em?

What you want to do is "normalize" your mp3 files. I did a quick search and came up with this page.

http://www.mp3machine.com/news/537/

I'm not sure about normalising the file, as far as my understanding of it is, normalising bases the whole file on the same peak which can mess up level differences in quiet softer and loud and brash sections. I'd use a program like Goldwave (i'm practically sure it's still free I haven't used it in a good five years). My other experience with normalising compressed audio files like MP3 is that you can gain signal noise or hiss depending on the amount of boosting needed and the compression rate.

As for midi I'm sure you could raise the volume of the midi track one by one to your preferred level in a master track or channel mixer, not sure if finale has this as i've never used finale, but in Cubase it's as standard, you could always import your midi into a version of Cubase if you have it and master the track and re export it to mp3.