Any technology that reproduces sound has at least two elements: a source and a destination. Often one or more additional intermediate elements are between the source and destination, such as a preamplifier that boosts volume level or an analog-to-digital or digital-to-analog converter, but you'll always have a program source and a destination device that converts the signal back to sound.
For example, consider an antique gramophone like the one shown in Figure 15-2. The source of the sound is a needle that follows the vibrations in a grooved disk, and the destination is a membrane that reproduces those vibrations through a horn.
In a modern music system, the program source can include the following:
Analog media such ...