Types of MediaThe documentation of sound information generally takes the form of some or another kind of magnetic or optical recording. We have witnessed an array of media formats for this purpose, ranging from phonograph cylinders and discs (which are neither magnetic nor optical in principle), to optical motion picture film sound tracks, to magnetic wire and tape, to, most recently, laser-optical digital compact discs. But by far, the currently preferred media for the recording of audio signals employ magnetic technologies.
Magnetic tape is the most widely used medium for audio recording. The type of information it stores can represent either analog or digital signals. With the advent of small, affordable digital computers, magnetic hard discs and other computer media are becoming increasingly popular as storage devices for digital audio data.
A Comparison of Analog and Digital FormatsAlthough it is true that analog and digital recording technologies, in comparison to one another, employ vastly different methods to store information, it is probable that the essential difference between the actual audio information produced by one, and that of the other, is a difference of degree, and not of kind. For it seems likely that, at the extreme lower limit of energy, all forms of energy, including sound, reach an impasse, in the shape of Planck's constant. It was the physicist Max Planck who, early in the twentieth century, determined that all energy must be quantized; that is, must occur at some discrete value; and it was he who determined the minimum possible value of energy.
Yet only well above this lower limit of energy value can the human ear distinguish changes in sound, and only well above this limit does any audio technology, be it analog or digital in principle, exert any practical controllable influence. The digital audio technology we use, however, operates with a finite set of possible values to which the audio signals it processes must conform. It is, then, primarily the forced quantization of the audio information to certain values of frequency and amplitude which distinguishes digital audio technology; whereas analog technologies, albeit theoretically constrained by the laws of quantum physics, employ no such method.