I have no idea. But the fact is that 128kbps is not a CD quality. I would suggest you to read more from r3mix website, it gives you a lot of information about the quality of MP3 compression.

You aren't wasting anything. When you rip a CD, you got a wav file which has 172 kilobytes per second data rate. It is five times more than hightest mp3 compression rate, 320 kilobits per second. Every time you compress wavs to mp3 form, you lose qualty. But if you use good codecs (for example Lame) and high enough bitrates, you won't be able to hear the difference between the original CD and compressed mp3 file.

If you wan't to have CD quality mp3 files, you need to use least 256kbps bitrate, or high quality VBR mode (which is able to lower the bitrate when the audio has higher compressiability, Lame with --r3mix preset is the best codec for this).