VWguy is right, recompressing an MP3 in a different codec or even a different MP3 bitrate will reduce quality. MP3 compression actually deletes certain inaudiable sounds to save space, but different codecs delete different sounds. Recompressing one lossy file that already has some information removed to an other lossy file will remove even more data. Recompressing a low bitrate file to a high bitrate file won't improve the quality at all because it can't recover the lost data, and it will in fact remove a little bit more.
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