Free MP3 Converter is a fully featured MP3 conversion utility. It is very easy to use, with a lot of options. It supports the encoding of .raw and .wav files, variable bit rates, adjustable bit rates (30-320 KHz), CPU priority management, IO frequency adjustment, sampling rates, different encoding modes (Mono, Stereo, Joint Stereo) and much more!
You can use our Free MP3 Converter together with Winamp (get it here) to rewrite some of your existing MP3's. The first step is to play the file with the output plugin called "Nullsoft Disk Writer plug-in". Then you can use Free MP3 Converter/Encoder to encode your .wav file into an MP3 according to your newly desired preferences. (Don't forget to change the output plugin BACK to whatever it was before.)