Re: arsclist Stereo or Mono Transfers of Mono Discs?

["George Brock-Nannestad" <pattac@xxxxxxxx>]

Date sent:      	Fri, 22 Jun 2001 15:29:06 -0700
From:           	Tom <tom@xxxxxxxxxxxx>
To:             	ARSCLIST@xxxxxxxxxxxxxxxx
Subject:        	arsclist Stereo or Mono Transfers of Mono Discs?
Send reply to:  	ARSCLIST@xxxxxxxxxxxxxxxx

> When making archival copies of 78s and mono 45s and LPs, should one
> make stereo or mono copies.


----- This opens a can of worms, and it not only depends on how 
you obtain your mono signal (by a dedicated mono pickup or a 
stereo signal summed). Several factor influence the result:

-- How was the original record cut? Was the tiny cutting face of the 
cutting stylus truly radial (which was usually the case for 
professional cutting with suction to remove the string of cut 
material - swarf in English, chips in American) or was it angled to 
direct the swarf toward the centre to be collected by a circular 
brush (which would be the case for private disc cutting)?

-- How is the replay today? Is it radial or tangential tracking? In 
radial tracking there are maximum two places (radii on the record) 
where the signal picked up from the two flanks of the groove are 
identical in time (no difference between them), provided the original 
groove was cut with a radial face to the cutting stylus. In tangential  
tracking the signals will be the same all the time, provided the 
stylus really travels along a radius.

-- Which kind of stylus is being used? Is it spherical or truncated 
elliptical or even line contact? If the latter is used, the vertical 
tracking angle has to be quite well fitted to the vertical tracking 
angle of the cutting stylus. Note that RCA Dynagroove was 
predistorted so that a spherical stylus is mandatory to obtain an 
undistorted signal.

You could say that by obtaining two signals, i.e. stereo, you can do
 more manipulations afterwards, and that may be an advantage. 
The quality of your stereo signal would depend very much on the 
channel separation over the whole frequency range (not just 1000 
Hz). Here optical replay via the ELP Laser Turntable may provide 
astounding results. For 78 rpm records it turns out to be an 
advantage to use mono left channel only, because that is in many 
cases much less noisy (worn) than the other. In such cases you 
would not want to use the other signal. 

However, the sound from a good stereo reproduction of a mono 
record using really good loudspeakers (electrostatics) is also 
astounding: provided the tracking and the angles mentioned are all 
well adjusted, the mono signal sits firmly straight in front of you, 
and the noise is distributed reasonably evenly and very much to the 
sides which means that you can focus better on the mono signal 
as such.

So all in all, I would generally prefer stereo, with the above provisos 
- at least until someone plays me a mono signal obtained via e.g. 
an Ortofon A or C head (a mono moving coil design with a very high 
vertical compliance).

I hope to have shed some light on the worms!

Kind regards

George Brock-Nannestad
Preservation Tactics