Sound is inherently analog, continuous in both time and value

Evidence

Sound is always an analog signal—that is, a function of time that has not been reduced to a finite set of numbers but instead takes on continuous values. Sound recording and playback were once analog throughout— for example, the sound pressure is turned into a stylus movement that carves a groove in tinfoil. In reverse, the stylus movement in the groove is communicated to a diaphragm and chamber at the throat of a horn (see figure 7.6 and section 7.3). Or, more twentieth century, the sound pressure is turned into an electrical signal (voltage), which then is used to align magnetic particles on the surface of a plastic tape. This is accomplished with a magnetic field created by the electrical signal at the recording head. When the tape is passed by a playback head, the process reverses, and the changing magnetic field due to the motion of the tape with its partially aligned magnetic particles creates an electrical current that, when amplified, is sent to loudspeakers. All this is analog at every step. — Eric J. Heller, Why You Hear What You Hear- An…, 480

Categorization

• DEFINE: Defines the analog nature of sound as continuous time-function and walks through the analog recording chain (mechanical to magnetic).