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