ANALOGUE TO DIGITAL CONVERTER
[Film Technology]
[Film Technology]
Analogue-To-Digital Converter or
ADC, an electronic device for converting data
from analogue to digital
form for use in electronic equipment such as digital
computers, digital audio recorders and digital video recorders, and communications equipment.
The conversion of analogue data to digital data form is now fundamental for all sorts of
everyday processes. Many phenomena in the physical world, for example the
intensity and colour of light or the intensity of sound
waves, vary in a continuous or analogue manner. Previously, the recording, transmission,
and manipulation of images and sound were executed by transforming the images
and sound into electrical voltages, whose
variations exactly mimicked changes in the original quantity. These
continuously varying electrical voltages were, in turn, manipulated in various
ways before being converted back to their original form. With the development
in the power of computers, however, it has become more convenient and
economical to convert these analogue signals to
digital form for the purposes of recording, transmission, and alteration, and then convert them back
to analogue form for their final use. A further advantage of the digital transmission and digital
manipulation of signals is that it can, to a large extent, prevent the
introduction of distortion and noise into the signal when it is transmitted and copied.
The process of analogue-to-digital conversion has two main stages. The first is
the “sampling” of the continuously varying
electrical waveform. In this context, sampling means measuring the voltage of
the signal at an extremely rapid fixed rate; in the case of music, for example,
the rate is usually 44.1 kHz (that is 44,100 times per second). The range that
these measurements cover is taken to be divided into a number of integral
increments or steps; in the case of music it is usually 65,534. In the second
stage, called “quantization”, the nearest of
these integral values to the actual value is assigned to represent the sampled value. The minute discrepancy between the
actual value of the measurement of the voltage and the integral value used is
called “quantization error”, and would be
perceptible if it were not largely eliminated by a further electronic process. Sampling and quantization
are usually done in the order just described for sound
recording purposes, but for use in television
and video recording they are done in the reverse
order inside the analogue-to-digital converter. The final stage of the
conversion is to express the integral number as a binary
digital number. A series of such digital numbers
is out-put by the converter, representing the digital form of the signal that
was input. All these processes are usually carried out within a single integrated chip.
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