[78-L] stereo/mono and noise reduction

[Michael Biel]

The Packburn worked by playing the quieter of the two groove walls, and
the later units played the sum of the two channels unless one wall was
quieter than the other.  There are some restoration engineers who either
prefer or occasionally use an old mono pickup instead of a stereo one to
eliminate any chance of getting vertical noise.  

Mike Biel  mbiel at mbiel.com  


-------- Original Message --------
Subject: [78-L] stereo/mono and noise reduction
From: DAVID BURNHAM <burnhamd at rogers.com>
Date: Fri, November 04, 2011 3:48 pm
To: "78-L at 78online.com" <78-L at 78online.com>

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.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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
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