Digital Music and Sound Quality
Sound is simply vibration of your eardrum, and thus can be represented as a graph with time on the horizontal axis and location of the eadrum on the vertical one. To record sound, this graph can be etched into the groves on vinyl records or converted into magnetic flux on tapes. Such representation, however, is difficult to copy, transmit, store, and analyze. Instead, digital systems record the coordinates of several points on the graph, and reconstruct the graph in order to play sound back to you in a connect-the-dots way. The more points are used, and the more precisely their coordinates recorded, the better the sound quality, but also the more space required to store the sound. This is why CDs sound better than MP3s, and hold music on a landline sounds better than on a cell phone. Click on the image to the right, to see increasingly accurate digital representations (in red) of a continuous curve (in blue).
Click on the image to the left, to see a direct conversion from an analog signal to a digital one.
Symphony No. 5 - Allegro con brio
performed by Skidmore College (courtesy of Musopen)To the left, are samples of the same audio track, recorded at different sample formats. Notice how as sound quality decreases, file size and sampling rate do so as well. This is essentailly because worse sound quality requires less information to be stored, and higher sound quality requires that more be stored. To make reference to the above graphs: while both are "jagged," the curve for the first audio track looks more smooth than the last one.
The "jaggedness" of digital signals (as seen in the above graphics) represents a loss of quality from the original sound being produced. In effect, even the highest quality recorded digital sample is of lower quality than the source sound.
Digital vs. Analog Sound: Why modern communication is digital
If the end result of digitization is lower sound quality, then why would someone ever store data digitally?
One answer is that analog data degrades easily: the effect of multiple small modifications (from media aging or interference during transmission) accumulates. In contrast, to change one number into another would require a dramatic deterioaration of the signal. That's why analog radio stations (such as the traditional FM) often have noise, while digital ones (such as HD or satellite) almost never do. Digital transmission and storage allow for long-term preservation and easy lossless copying (and thus give headaches to the content industry, whose business depends on the exclusive ability to copy).
Another answer is that digital data is more easily manipulated. It can, for example, be encoded with error-detecting or error-correcting codes to further guard against loss, encrypted for privacy or digital rights management, or routed over a packet-swtiched network, such as the Internet.