Does anyone know of a program I can use to reduce the bitrate of MP3s without having to re-record off of the origional CD?
Well, first a note about quality: Obviously you are ok with reducing the quality, presumably to save space, but you should know that if you convert mp3 to mp3, your resultant mp3s will be of a considerably lower quality than if they had been encoded at your target bitrate to begin with. How much lower depends on what bitrate you are targeting and what bitrate you are converting from. Just so you know.
That said, your best bet is just to convert them to WAV using the WinAMP Disk-Writer output plugin, then reencode using your favorite mp3 producing software–almost all of them convert WAV files. Alternatively, I believe there are some WinAMP plugins that will convert mp3 to mp3, so you can just set up a playlist and hit “play.” Search winamp.com under output plugins for “mp3 writer.”
LAME will do what you want. LAME also has the distinction of being the highest quality MP3 encoder. It is command-line driven, so read the USAGE file for full details. In short, the easiest command is:
LAME --mp3input -b newbitrate infilename.mp3 outfilename.mp3
For slightly slower performance but higher audio quality, use:
LAME -q 0 -d --mp3input -b newbitrate infilename.mp3 outfilename.mp3
Hope this helps.