[78-L] stereo/mono and noise reduction

[DAVID BURNHAM]

dl wrote:

This doesn't answer your question, but there's another trick I learned years 
ago from an "audio for idiots" column which advised using a Surround System 
Receiver and taking the mono audio from the dolby pro logic, which would result 
in a quiet sound from otherwise noisy mono discs. He was talking about 45s but 
I got myself one of those units and it immediately proved to be wonderful on 
78s, especially reducing rumble on laminated Columbias. (If someone needs a 78 
transferred in stereo, I go back to the stereo output..this also enables me to 
do a cross fade if one side of a groove is noisier at the start and the other 
side is noisier at the end.


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This isn't a perfect solution but it can be very effective on some material.  I have a Waves Audio plug-in called "Centre";  this is a plug-in which can reduce or increase the side elements or the centre elements independently in a stereo file.  I have played a 78 through it in stereo and reduced the side elements to zero;  what remains is a fairly clean signal of the music.  Switching the bypass switch on and off seems to just turn the noise on and off.  This works because few if any noise elements on a record are in true mono;  for that to be the case, the damage to the groove wall causing the noise would have to be identical on each side of the groove but out of phase - a bump on one side of the groove would have to have a crater on the other side of the groove of the same dimensions.  Just tying the channels together into mono will remove any noise which is truly vertical but doesn't achieve the same degree of noise reduction because an
 element on one channel only will still cause lateral displacement of the stylus and be included in the signal.

db