Joyce Brite had requested info on removing scratch sounds from vinyl
and LP recordings. Back in the "Good old days" (1970s, I guess) there
was a company which produced an audio device which sampled incoming
signals (phono record signals, e.g.) on a constant basis (many times
per second). When the sample showed a variation from the preceding
sample, it checked the next sample. If the third sample matched the
first sample, the second sample was eliminated.
If I remember correctly, only certain frequencies, which corresponded
to frequencies produced by a scratch, were those examined and/or
eliminated. A highly scratched record could come out sounding
wonderful. There was also built in a switch to hear what had been
removed by the filter. It did not remove constant hissing sounds,
This device cost between $200-$300 at the time, a bit expensive.
I have no idea of its manufacturer or its actual name, but was
impressed with the way that it operated. There should be a few of
these still floating about, or some other company should have the
same type of filtering device available.
Best wishes, Mike Walter