Joel Selvin, San Francisco Chronicle Senior Pop Music Critic

Whether you know it or not, that compact disc you just copied to your MP3 player is only partially there.

With the CD on its way out and computer files taking over as the primary means of hearing recorded music, the artificial audio of MP3s is quickly becoming the primary way people listen to music. Apple already has sold 100 million iPods, and more than a billion MP3 files are traded every month through the Internet.

• [ MP3: Just because it's digital, doesn't mean it sounds good.] (podcast link illustrating the degradition in sound quality as file sizes are reduced) 

But the music contained in these computer files represents less than 10 percent of the original music on the CDs. In its journey from CD to MP3 player, the music has been compressed by eliminating data that computer analysis deems redundant, squeezed down until it fits through the Internet pipeline.

When even the full files on the CDs contain less than half the information stored to studio hard drives during recording, these compressed MP3s represent a minuscule fraction of the actual recording. For purists, it's the dark ages of recorded sound. 

• read the whole article here