Though MP3 files have the same sampling rate as CDs (44.1 kHz), they use a compression process that shrinks the file to about 10 percent the size of an equivalent track on a compact disc.
The file size is reduced through digital compression. This process tends to "smudge" distinct, individual sounds together into a sonic "clutter."
This sonic "clutter" loses "variation in rhythm, pitch and loudness," notes Daniel Levitin, a professor of neuroscience and music at McGill University. The sound becomes monotonous and ultimately fatigues the brain.
The MP3 format is also notorious for eliminating the low- and high-pitch frequencies found in the master recording.
The difference between CD and MP3 quality is not as significant as that of CD and vinyl LPs. The analog sound produced by a high-quality turntable is far "warmer" and less subject to distortion from high-level (i.e. loud) signals.