This article is from the Audio Professional FAQ, by with numerous contributions by Gabe M. Wiener others.
Digital techniques have been applied to many facets of sound processing
and recording and have, on the whole, been found to give results far
superior to their analogue counterparts. Nowhere is this more true than
in the field of audio restoration, where excellent processes have been
developed for removal of impulsive noise (thumps, clicks and ticks) and
attenuation of continuous broadband noise (such as tape hiss). Example
techniques for these two are outlined below.
 
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