Now that the WAV are now normalized you got to make them MP3's again. This is where our second free program comes in. The program is called CDex.
First thing to do is to select 'options' in the menu, then 'settings'.
From here you can select different option to encode your mp3s.
Make sure the encoder is using the Lame MP3 encoder and the bitrate is the same as your mp3's were before you made them WAVs.
If you don't know your bitrate of your mp3's they're most likely 128, 160, or 192. the rest of the default settings you can leave alone.
Next thing to do is to open up the directory of your normalized WAV files by pressing the fourth button down on the right side.
Select the WAV files and press convert. Again this will take a few minutes. When it's done you can find your new normalized MP3's in the default Cdex directory.
You may have noticed that Cdex can also normalize. the reason i suggested MMwave was simply because the program is geared towards normalizing only and i think it does a better job.
Try both and decide which one you like better. If you use Cdex to do the whole process, it basically the same process as using mmwave.
1-convert you mp3's to WAV files using CDex (5 button down on the right)
2-make sure your settings are okay to encode
3-select your WAV files and this time check the normalize box
4-press the convert button