analog-to-digital conversion

analog-to-digital conversion the process of changing continuously varying data, such as voltage, current, or shaft rotation, into discrete digital quantities that represent the magnitude of the data compared to a standard or reference at the moment the conversion is made. There are two types of converters: electromechanical—also called shaft- or position-to-digital—and electronic. The most common use is to change analog signals into a form that can be manipulated by a digital computer , as in data communications; a modem , or data set, is a device that converts the digital signals produced by computers and terminals into analog signals that telephone circuits are designed to carry and then back to digital signals at the other end of the communication link. Similarly, in digital sound recording, audio signals are transformed into digital data, which are then recorded on a magnetic or optical disk or tape; the digitized data on the recording medium then must be changed back into the analog sound signals that can be used by a stereophonic sound system. See also digital-to-analog conversion .

Bibliography: See M. J. Demler, High-Speed Analog-to-Digital Conversion (1991); K. M. Daugherty, Analog-to-Digital Conversion: A Practical Approach (1995).

digitize
1. To translate graphical information into a series of numbers suitable for processing by (digital) computer. For example, topographic detail can be taken from a map and digitized to produce a computer-generated topographic cross-section. The superimposition of an orthogonal coordinate system on to an image and the recording of the data in a machine-readable form assumes that a two-dimensional image is being analysed. It can be done three-dimensionally if stereophotographs are analysed. Fully automated systems also exist for this type of work.

2. To convert analog data into digital form by sampling the continuous record at discrete sample intervals. See also ALIASING; and SAMPLING FREQUENCY.

dig·it·al / ˈdijitl/ • adj. 1. relating to or using signals or information represented by discrete values (digits) of a physical quantity, such as voltage or magnetic polarization, to represent arithmetic numbers or approximations to numbers from a continuum or logical expressions and variables: digital TV. Often contrasted with analog. ∎  (of a clock or watch) showing the time by means of displayed digits rather than hands or a pointer. 2. of or relating to a finger or fingers. DERIVATIVES: dig·it·al·ly adv.