The digitization of sound is a fairly straightforward example of the processes of quantization and sampling described in Chapter 2. Since these operations are carried out in electronic analogueto- digital converters, the sound information must be converted to an electrical signal before it can be digitized. This can be done by a microphone or other transducer, such as a guitar pickup, just as it is for analogue recording or broadcasting.
Increasingly, digital audio, especially music, is stored in files that can be manipulated like other data. In particular, digital audio files can be stored on servers and downloaded or distributed as “podcasts” (see Chapter 16). Digital audio players, such as Apple’s iPod, store such files on their internal hard disks or flash memory. Almost always, audio in this form is compressed.
Contemporary formats for digital audio are influenced by the CD format, which dominated audio for over two decades. For instance, the sampling rate and number of quantization levels used for high-quality audio is almost always the same as that used for CD. (Despite the journalistic habit of distinguishing between CD and “digital” music, CD audio is, of course, digital.)