MP3 is known as a "lossy" format because it removes audio information in order to reduce file sizes, even at the maximum 320kbps rate. By comparison, FLAC is a "lossless" format because it doesn't remove info and instead compresses music in a similar way to a ZIP file. As a result, a FLAC sounds better than an MP3, especially one that's been ripped at a low 128-kbps bit rate.