The background hissing noise ...
Radio signals from the surface of the sun or other astronomical radio sources
Any warm or hot electronic component
Carbon film resistors
Residue signals from the Big Bang!
Regenerating Digital Signals
Digital signals can be cleaned up, restoring the original signal perfectly, as long as the noise level is not too great.
Once the noise is too bad, the digital signal "breaks up" into video rectancles or audio burbles, squeeks or gaps.
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