Two replies in one here ...
On Wed, 09 Nov 2011 14:40:12 +0000 (GMT), Jim Lesurf
wrote:
You may be overlooking the fact that the test LPs I used were also cut and
pressed. But I agree that these may have been made with much more care than
ye olde EMI knock-outs.
Yes, but I was wondering (I admit I hadn't really thought about it
much) if some special steps beyond my knowledge might have been taken
to produce something sufficiently good that it could be used to
measure effectively only the playback distortion. So we are to
presume, then, that the tones on test LPs are simply guaranteed 'pure'
before being cut and pressed, but by the time they get to the end-user
they contain all the normal distortions of cutting and pressing?
Alas, overall the AES and its members has long lost interest in LP.
Alas? I really can't say I blame them. The only interest I have in
vinyls is saving the recordings off my own as best I can.
The
closest you get is people using things like laser scanners and optical
systems to read old discs and process them into audio.
Yes, I've heard of such systems. Presumably their cost is massive.
But there were many
measurements and sets of analysis in the past. The bottom line, though, is
that it varies a lot from one LP to another - to the point pun that which
stylus/cart/geometry works best for one LP won't be best for another. Not
just a matter of cutting angles, etc. Also questions like the elasticity
and elastic limits of the specific 'vinyl' sic used for that LP.
Yes, I've noticed many variations in quality - not just between the
decks, which I suspect is mainly due to the cartridge/stylus pairings,
but also between vinyls. Most noticeable are differences in volume.
Some are unusually quiet, others unusually loud.
One of the reasons most AES members stopped taking an interest in
'analogue' is that they got very aggressive abuse from some audio
enthusiasts when they showed they doubted what some 'golden ears' and
'high end' makers claimed.
Yes. While I suspect that none of us are completely clear of guilt
(last night, one of Rob's posts so exasperated me that I did a burn,
which is perhaps regrettable), I suspect those who can't support
themselves by logic are vastly more prone to resorting to abuse.
Perhaps I should out on my (long) 'to do' list a review of what was
measured and published in the past about topics like LP distortion. I did
deal with noise and dynamic range, but that is easier to summarise.
It would certainly be good to have something authoritative. Were
there any similar publications concerning open-reel and AC?
However I chose the bands that step or sweep
the frequency or level to probe how that changed the distortion.
Making tests with a single tone isn't that revealing. It would make more
sense IMHO to use a set of tones that would represent something like an
equal-tempered chord. (i.e. with no simple integer ratio between all the
components). That helps get away from the idea that the distortion must be
pleasing as it is 'just second harmonic'. Yes, that does just tweak the
harmonics for a single note on an idealised instrument. But in reality,
music isn't so simple. :-) Alas, no-one makes an appropriate test LP.
Yes, I suspect that I was thinking along similar lines when I first
discovered the page and marked it down in my mind as 'not
authoritative'. The tests seemed too simple, and the narrative seemed
to be trying to pander too obviously to vinyl enthusiasts. Even so,
7%!
I seem to remember something about square waves - by Fourier's
Theorem, a periodic square wave can be represented by an infinite
series of sine waves. Thus, a square wave contains all the harmonics
above the fundamental. Thus, distortion is easily measured by
inputting a square wave and seeing what shape of wave comes out, any
departure from 'squarity' showing how harmonics have been mangled by
the system. Therefore by sweeping frequencies of square waves through
a system, one measures THD against frequency, and gets the sort of
plots displayed on your page. Is my memory correct, is that how it's
done?
If you test *difference* component (i.e. vertical motion) you may well find
the result isn't mainly second-order. As with FM, stereo makes a lot of
difference pun. ;-
However it is very hard to predict this as it varies such a lot from one
example to another.
Yes, there are so many variables in a vinyl system - cutter, press,
vinyl material, turntable mechanics, tone-arm mechanics + wiring,
cartridge + stylus, preamp. When you consider how all these vary
significantly, it's a wonder that vinyl could ever be as good as it
sometimes was.
For me though, the killer thing with all analogue recording systems,
is the fragility of the media. So many vinyls that I've since given
away to charity shops got heartbreaking scratches, so many open-real
recordings got the tape mangled. And of course, Sod's Law nearly
always dictated that these were in my favourite tracks - because
they were my favourite tracks, they were the ones being played most
often, so if there was going to be damage, it would most probably
happen to them.
What did seem sad to me was that an ancient V15 should
do so well compared with modern designs.
Yes, that's really rather shocking, especially that you can't even get
pukka replacement styli for them. It says to me that manufacturers
are thinking: "Noone who cares about quality still uses vinyl, so
we'll concentrate on producing something that is easy and cheap to
make, and if that means that it is not as good as former designs, so
be it. No one that matters will notice!"
I'm glad that I didn't have to rely on the presumed ceramic cartridge
of the Project. The Shure is so unmistakably better. I did consider
putting it in the Project deck, which would probably have been the
simplest solution, but this particular Shure is mounted in the Dual
cartridge holder by a plastic clip arrangement rather than the usual
pair of screws, and I would have had to hack this off to be able to
mount it in the Project. I took fright at that point, thinking that
hacking the deck was probably going to be the easier option, though it
was all my aging fingers could do to achieve such delicate soldering.
Also, I suspect that the preamp in the Project deck is matched to the
cartridge, so there is no guarantee that I would have got the amount
of improvement that could be anticipated from the change.
--
================================================== =======
Please always reply to ng as the email in this post's
header does not exist. Or use a contact address at:
http://www.macfh.co.uk/JavaJive/JavaJive.html
http://www.macfh.co.uk/Macfarlane/Macfarlane.html
Digitising Vinyls (OT for uk.tech.digital-tv)
Linear Mode
