Hi
Why mess with Mp3 . they are so yesterday.
Stick to wave files.
Better for your lug holes.
If you must have mp3 go for
FORMAT FACTORY .It is free and just scan the download with an anti- virus program as sometimes free programs carry viruses.
When loading up Format Factory make sure you untick all the extras as they are adware rubbish.
You can do all sound files including flac and also you can convert movie files from downloads if you have a great
VPN.You can also put sound files in Cubase or any Daw and nomalize and output to whatever output file you want
Audacity also converts normalizes etc and that is a great free program