“People used to sit and listen to music,” Mr. Fremer said, but the increased portability has altered the way people experience recorded music. “It was an activity. It is no longer consumed as an event that you pay attention to.”
Instead, music is often carried from place to place, played in the background while the consumer does something else — exercising, commuting or cooking dinner.
The songs themselves are usually saved on the digital devices in a compressed format, often as an AAC or MP3 file. That compression shrinks the size of the file, eliminating some of the sounds and range contained on a CD while allowing more songs to be saved on the device and reducing download times.
via A Musical Revolution, With a Cost in Fidelity – NYTimes.com.