The advent of MPEG 1, Audio Layer 3 (MP3s) as the most popular music compression format in the mainstream Internet community several short years ago changed the face of music as we all know it. Net-savvy music-lovers found out that, using the so-called MP3 format, 60 minutes of near-CD quality audio could be packed onto roughly 60MB (or less) of disk space on their hard drives. Considering this would require roughly 600MB on a standard CD, the discovery was well worth the find.
Music compressed into MP3 format (encoded to MP3) does have a few limitations however. For one, it's "lossy." Just like those smudgy, blurry Jpegs you see all over the net, the quality of an MP3 file is reduced from the high-fidelity original of a CD. The most telling comparison is in a value known as the bit-rate. The bit rate coding stream of a standard CD is 705kbps (kilobits per second) per channel. Widely accepted as "CD-Quality" on the net, most high-quality MP3s are encoded at 128kbps, similar to Minidisc's ATRAC method. The lower the bit rate, the smaller the file, and unfortunately, the lower the sound quality.
Whether or not the resultant artifacts can be heard largely depends on the type of song being played. Personally, I find MP3s with smooth, round midrange and thick, slow bass less lively than their polycarbonate cousins, whereas fast titles with peaked beats, rhythm, and greater dynamic range transfer well to the Mpeg format. I'm not quite sure how the sound of a Quake rocket launcher would sound, but then I'm not the one who listens to game recordings at night in order to "become one" with the mouse.