Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!sdd.hp.com!spool.mu.edu!uwm.edu!csd4.csd.uwm.edu!info-high-audio-request
From: Steve_Graham@ub.cc.umich.edu
Newsgroups: rec.audio.high-end
Subject: VTA
Message-ID: <10122@uwm.edu>
Date: 11 Mar 91 13:52:17 GMT
Sender: news@uwm.edu
Lines: 52
Approved: tjk@csd4.csd.uwm.edu
Originator: tjk@csd4.csd.uwm.edu

This is a sticky subject.  In my own less-than-state-of-the-art system I've
been able to drive myself nuts trying to get it right, without ever coming
to any concrete conclusions.  In general, I do have the impression that if
it's too high (back of the arm, that is) the sound is a little bright and
spitty, and too low, it's sort of overdamped sounding, a sort of slight  
muffling effect.  But it's really hard to set the thing for a variety of
reasons.  For one thing, I find that I can hear what's going on far more
clearly when I'm just listening to the music for enjoyment than when I'm trying
to listen critically.  (This is also a problem when I am trying to set up
mikes and balances for recordings.  I think it is a problem in the professional
recording industry to a degree that is not generally acknowledged--but you can
chalk it up as just one of SG's hair-brained theories if you like.)  So when
making adjustments it's just plain hard to be certain that I'm hearing a
difference.
 
Then there's the hardware problem.  In the early days of stereo disks, the
Westrex cutter was quite popular, and had a fairly fixed cutting angle of
23 degrees.  Later 15 degrees became a standard, though it is not clear to me
whether (or to what extent) it was adhered to.  Later on 20 degrees was
set as a new and improved standard.  (I don't know the reasons for this, not
having any cutting experience.)  Again I don't know how closely this was
adhered to.  More recently we have DMM cutting, which cannot be done at these
angles.  What is done instead is to cut at approx. 0 degrees, and then add
some form of electronic compensation to "simulate" the 20 degree nominal
standard angle.  Complications abound.  First DMM: I don't know exactly
how the compensation works, but I assume it is a form of predistortion,
similar to what is sometimes added to prevent or reduce inner groove distortion.
The way this works is that you generate a distortion product that is out of
phase with the one the stylus will generate, and the two cancel each other
out.  However anything that relies on this sort of cancellation is hard to
get right.  Everything has to be just right for it to work.  In this case,
it will only work for a stylus of particular dimensions.  With others there
may be a lessening of distortion, or even an increase under some circumstances.
I suspect there is a similar situation with DMM, to the extent that the thing
works at all.
 
Then there are the lacquer and vinyl problems.  Both the lacquer medium which
is used for non-DMM cuts, and the vinyl pressings themselves, will vary the
apparent tracking angle to a certain degree.  I gather that with the lacquers
the degree of change is dependent to some extent on how soon plating takes
place, and storage temperature, etc., though I'm no expert on this.  But
the point of all this rambling is that there is a rather wide divergence
of proper tracking angles between disks.  So the people who reset for each
disk have the right idea...though I'm not willing to go that far myself.
 
Since he is my favourite musician, I generally use a Bruce Cockburn LP to
try to set VTA.  Several of his records were cut at the same place and pressed
by the same people, so I have a chance of getting it close on at least a few
of my favourite records, and since those were cut at Sterling Sound or
Masterdisk, and pressed by one of the majors, they will hopefully be close
to other records in my collection.  On the other hand, I may not be hearing
those old RCAs to best advantage.  Such is life.