Unlike analogue electrical line level audio signals, which exactly mimic the shape and changing pressure of an air pressure soundwave in electrical form, digital audio signals consist of a simple pulse wave which represents a binary data stream that describes the wave shape in mathematical terms. They therefore cannot be said to be audible until they are converted, or decoded, back to an electrical signal. The process of converting an electrical line level audio signal to digital is known as analogue to digital conversion, or A to D. The process of converting an digital audio signal to electrical line level is known as digital to analogue conversion, or D to A.
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