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 Post subject: Noise Reduction --- How Is It Done?
PostPosted: Dec Thu 07, 2017 5:04 pm 
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Joined: Feb Sat 12, 2011 2:29 pm
Posts: 421
Location: Fayette County, Pa
I have a stack of old 78s that are about in what would be considered average for their age. (Most are very early 1900s - 1920s.)

I visited the website listed elsewhere on this forum and some are the same copies as what I have. When I download them in many cases they are clean; virtually no surface noise at all yet maintain their frequency response within what would be expected for the time. Even the surface noise that was present when new had been eliminated. Obviously they were done by professionals to obtain this level of quality. My question is how is it done? What steps are taken to obtain this level of restoration? Obviously it goes beyond just running them through a computer program like Audacity, etc. , I am curious what additional steps they do to obtain this clarity to something that never was this good even when new?


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 Post subject: Re: Noise Reduction --- How Is It Done?
PostPosted: Dec Fri 08, 2017 3:52 am 
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Joined: Sep Tue 30, 2014 6:08 am
Posts: 2071
Location: The Old Dominion VA 23518
Back in 2012, I saw a display at the Smithsonian Museum of American History where lasers were "reading" a vinyl disc that was also "mapped by another laser that found the best area to read, so perhaps a laser was used. According to the display, the use of lasers was brought about to make new masters where an LP existed, but no master disc or tape could be found. The whole thing was sponsored as a "future tech" feature in each room of the exhibit. Apple, Sony, and either BMI or EMI sponsored the sound exhibit.

Aside from lasers, modern digital signal processing can "clean up" just about any dirty waveform, and with only femto-second delays. With a laser "map" of the un-damaged areas of a record groove, you could read the disc with a laser, send it through all the filters (scratch, rumble, etc) and yield an ear-clean recording.

I'll admit this is as far as my interest can take me. Being hearing impaired, I have no need for hifi or audiophile quality anything.... :(

_________________
Brian
"Capacitor Cosmetologist since 1979"
USN Retired 1984-2006 (Avionics/Cal)


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