Arced Positional Error of stylus tracking a spiral groove ..

Archived from groups: rec.audio.pro (More info?)

On a conventional disc player, assuming its speed is the same as media
disc-cutter....
The tone arm (say 11" from pivot to stylus) is dragged via its stylus
through an arc segment from outer groove to inner groove during its course
of play. Ideally it should travel radially in a straight line as the master
was cut that way - and it would track the usable grooved portion at a
tangent.
This delta alteration would generate tiny pitch dopplers related to the
distance from the next-expected location of reference per rev. It passes
through a maximum deviation and retreats again in a curvature. Therefore,
there are generally only two points where the stylus is where it ought to be
for those radii.

Is there a proper technical word for describing this phenomenal parameter
that arises from an all-too-frequent occurrence? I have never seen discussed
the altered-pitch aspect derived from the well-known tracking error. It must
be related to wow!
Not to mention the angular errors that result in slewing from the true
tangent.

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On Sat, 21 May 2005 15:22:55 GMT, "Jim Gregory"
<jim.greg@ntlworld.com> wrote:

>On a conventional disc player, assuming its speed is the same as media
>disc-cutter....
>The tone arm (say 11" from pivot to stylus) is dragged via its stylus
>through an arc segment from outer groove to inner groove during its course
>of play. Ideally it should travel radially in a straight line as the master
>was cut that way - and it would track the usable grooved portion at a
>tangent.
>This delta alteration would generate tiny pitch dopplers related to the
>distance from the next-expected location of reference per rev. It passes
>through a maximum deviation and retreats again in a curvature. Therefore,
>there are generally only two points where the stylus is where it ought to be
>for those radii.
>
>Is there a proper technical word for describing this phenomenal parameter
>that arises from an all-too-frequent occurrence? I have never seen discussed
>the altered-pitch aspect derived from the well-known tracking error. It must
>be related to wow!
>Not to mention the angular errors that result in slewing from the true
>tangent.
>
Interesting thoughts. OK, you are advocating linear trackers, then

-- But this error, if noticeably existing in the real world, could be
measured by a test record having a perfectly cut sine wave -- say abt.
3.150 Hz -- and a deviation meter bridge connected to a paper
recorder. If the line would go astray -- then you'd proof the
behaviour. But I've never noticed a change in pitch even at largest
sustained notes. The problem with a wow is far more common, either due
to poor reproduction, or the record being pressed not in perfect
center.

Interestingly, at really old shellack records (I won't say "78 RPM"
here as in many cases it is not that speed) , I notice changes in
pitch. But sometimes the cutting table has been cranked by hand -- so
I take it for normal. Or later, when there were frequencies not
exactly 50 or 60 Hz, the records can play at a different pitch today.
Even old tapes, especially those dubbed on different machines, are
often suspectible for a correct pitch. I While correcting a pitch of
an otherwise well rotating record or tape is relatively easy (and
required at many old recordings), it is really hard to correct
variations of pitch, that "wow". Perhaps impossible to do it the
perfect way.

Edi Zubovic, Crikvenica, Croatia

Archived from groups: rec.audio.pro (More info?)

> No, not advocating any linear radial tracker, I realise that is the answer
> to complement cutter route, but I'm just trying to get any info on this
> *phenomenon*!
> Yet, if using a conventional (but wrong) tone arm, the pitch/velocity
> error is not commonly audible but is just measurable.

I've thought about this, but I don't see how the "tracking" error can introduce
a speed change, cyclic or not. The disk, after all is rotating at a constant
velocity, and any speed error would have to be cyclic. If it is, it occurs
slowly, over many seconds, as the arm passes through greater or lesser amounts
of deviation from perfect tangency.

What the tracking error does introduce (besides harmonic distortion due to
increased tracing error) is relative timing errors between the channels that
increases and decreases as the tracking error increases and decreases. But it's
a small effect, and I've never heard anyone claim it was audible. It certainly
doesn't show up when playing quadraphonic recordings.

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On Sun, 22 May 2005 04:28:24 -0700, "William Sommerwerck"
<williams@nwlink.com> wrote:

>> No, not advocating any linear radial tracker, I realise that is the answer
>> to complement cutter route, but I'm just trying to get any info on this
>> *phenomenon*!
>> Yet, if using a conventional (but wrong) tone arm, the pitch/velocity
>> error is not commonly audible but is just measurable.
>
>I've thought about this, but I don't see how the "tracking" error can introduce
>a speed change, cyclic or not. The disk, after all is rotating at a constant
>velocity, and any speed error would have to be cyclic. If it is, it occurs
>slowly, over many seconds, as the arm passes through greater or lesser amounts
>of deviation from perfect tangency.
>
>What the tracking error does introduce (besides harmonic distortion due to
>increased tracing error) is relative timing errors between the channels that
>increases and decreases as the tracking error increases and decreases. But it's
>a small effect, and I've never heard anyone claim it was audible. It certainly
>doesn't show up when playing quadraphonic recordings.

-- There is an issue regarding geometrical distorsion; this can be a
problem per se indeed. This has been measured by help of a measuring
record (in Europe, acc. to DIN 45 542) where a 3 kHz + 300 Hz
frequency pair has been cut onto and and a flutter meter such as EMT
424. Depending on quality of a cartridge, this 3 kHz signal is being
less or more modulated with 300 Hz. A measure of geometrical
distorsions is called FIM, frequency modulation factor. As these
distorsions are due to phase modulation, they are a kind of frequency
modulation, hence the name.

Edi Zubovic, Crikvenica, Croatia

Archived from groups: rec.audio.pro (More info?)

William Sommerwerck <williams@nwlink.com> wrote:
>> No, not advocating any linear radial tracker, I realise that is the answer
>> to complement cutter route, but I'm just trying to get any info on this
>> *phenomenon*!
>> Yet, if using a conventional (but wrong) tone arm, the pitch/velocity
>> error is not commonly audible but is just measurable.
>
>I've thought about this, but I don't see how the "tracking" error can introduce
>a speed change, cyclic or not. The disk, after all is rotating at a constant
>velocity, and any speed error would have to be cyclic. If it is, it occurs
>slowly, over many seconds, as the arm passes through greater or lesser amounts
>of deviation from perfect tangency.

Right, and if this DOES exist, it can easily be measured with a test tone
record that has the same tone at the inner and outer grooves, like the
Shure S15. A frequency counter and a test record will tell you a lot.

Personally, I'd just be happy for the &^%$%^&^&%! plant to get the hole
centered.

>What the tracking error does introduce (besides harmonic distortion due to
>increased tracing error) is relative timing errors between the channels that
>increases and decreases as the tracking error increases and decreases. But it's
>a small effect, and I've never heard anyone claim it was audible. It certainly
>doesn't show up when playing quadraphonic recordings.

This is a miniscule effect since the difference in spacing is a fraction of
a mil. I seriously doubt if it would be as much as a full wave at 10 KHz
even worst-case. But if you're worried about it, leave a big lead-out!
--scott
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

Edi Zubovic <edi.zubovic[rem this].@ri.htnet.hr> wrote:

> On Sun, 22 May 2005 13:11:12 +0100, poppy.uk@ukonline.invalid.invalid
> (Adrian Tuddenham) wrote:
>
> >Edi Zubovic <edi.zubovic[rem this].@ri.htnet.hr> wrote:
> >
> >
> >> ...
> >> Interestingly, at really old shellack records (I won't say "78 RPM"
> >> here as in many cases it is not that speed) , I notice changes in
> >> pitch. But sometimes the cutting table has been cranked by hand
> >
> >Only the very first experimental disc recording machines were
> >hand-cranked. As far as I know, all comercial records up to the 1920s
> >were made on weight-driven machines with very stable governors and an
> >extremely steady speed (which wasn't always 78 rpm, as you correctly
> >state). Some weight-motor lathes continued to be used into the 1950s.
> >
> >If you are hearing wow, it is probably because the pressing has its hole
> >off-centre. During the manufacturing process, the location of the
> >centre was lost and it had to be re-marked and drilled manually on each
> >stamper. This was done to a degree of accuracy which depended on the
> >mood of the centre-drill lathe operator.
>
> Oh, I see. Thanks for a bit of useful info. Speaking of off-centre
> holes, wasn't it a Nakamichi (if I recall it right) turntable model
> which has been so to say self-centering?

That sounds interesting, but I really don't know.

My set-up for 78s is a home-designed parallel tracking arm where the
carriage servo motor can be switched off and the optical arm-angle
sensor connected to a large analogue meter. By revolving the turntable
slowly, the swing of the grooves can be read off the meter and corrected
by carefully sliding the disc.

I may have invented the "Wobbleometer".

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

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"Edi Zubovic" <edi.zubovic[rem this].@ri.htnet.hr> wrote in message
news:52u091dtgt1g7aignm77rkvrbobi452fq5@4ax.com...

> Oh, I see. Thanks for a bit of useful info. Speaking of off-centre
> holes, wasn't it a Nakamichi (if I recall it right) turntable model
> which has been so to say self-centering?

Yes; it was quite clunky to operate, but it worked.

Peace,
Paul

Archived from groups: rec.audio.pro (More info?)

> It can make a big difference to the way some types of 78s de-clickers
> differentiate between signal and click. If the 'azimuth' is slightly
> out of alignment and you use a truncated elliptical stylus, the change
> in pinch effect alters the 'S' signal considerably (the increase is not
> so obvious on a conical stylus).

I assume you're referring to the model (I forget the name) that switches between
channels to get a better signal. (Before the rest of you write in, we're talking
about playing a mono disk with a stereo pickup.)

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William Sommerwerck <williams@nwlink.com> wrote:

> > It can make a big difference to the way some types of 78s de-clickers
> > differentiate between signal and click. If the 'azimuth' is slightly
> > out of alignment and you use a truncated elliptical stylus, the change
> > in pinch effect alters the 'S' signal considerably (the increase is not
> > so obvious on a conical stylus).
>
> I assume you're referring to the model (I forget the name) that switches
> between channels to get a better signal. (Before the rest of you write in,
> we're talking about playing a mono disk with a stereo pickup.)

The "Packburn" is probably the one you are thinking of , but there is
also the "Mousetrap" by Ted Kendall which works in a similar way and
the one without a name that I invented, which works slightly
differently.

My experience is based on my own de-clicker, but the principle would
apply to the others, too, because (as you point out) they all use a
stereo pickup signal to de-click mono; so the vertical signal component
is critical for distinguishing the laterally recorded mono signal from
post-recording noise.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Archived from groups: rec.audio.pro (More info?)

William Sommerwerck <williams@nwlink.com> wrote:
>> It can make a big difference to the way some types of 78s de-clickers
>> differentiate between signal and click. If the 'azimuth' is slightly
>> out of alignment and you use a truncated elliptical stylus, the change
>> in pinch effect alters the 'S' signal considerably (the increase is not
>> so obvious on a conical stylus).
>
>I assume you're referring to the model (I forget the name) that switches between
>channels to get a better signal. (Before the rest of you write in, we're talking
>about playing a mono disk with a stereo pickup.)

No, he's not talking about the Packburn. He's saying that if there is a
change in the top end (like tape azimuth error), the clicks and pops will
not be as sharply defined and won't be as easily detected by the software.

I don't think this is actually the case because I don't think it will affect
the clicks, which are not necessarily correlated between groove sides, just
the signal, which is correlated.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

In article <1191l4r9mreuke7@corp.supernews.com> williams@nwlink.com writes:

> I assume you're referring to the model (I forget the name) that switches
> between
> channels to get a better signal.

The Packburn noise reducer?

--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo

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Scott Dorsey <kludge@panix.com> wrote:

> William Sommerwerck <williams@nwlink.com> wrote:
> >> It can make a big difference to the way some types of 78s de-clickers
> >> differentiate between signal and click. If the 'azimuth' is slightly
> >> out of alignment and you use a truncated elliptical stylus, the change
> >> in pinch effect alters the 'S' signal considerably (the increase is not
> >> so obvious on a conical stylus).
> >
> >I assume you're referring to the model (I forget the name) that
> > switches between channels to get a better signal. (Before the rest
> > of you write in, we're talking about playing a mono disk with
> > a stereo pickup.)
> No, he's not talking about the Packburn. He's saying that if there is a
> change in the top end (like tape azimuth error), the clicks and pops will
> not be as sharply defined and won't be as easily detected by the software.
>
> I don't think this is actually the case because I don't think it will affect
> the clicks, which are not necessarily correlated between groove sides, just
> the signal, which is correlated.

The problem is not with the clicks and pops, which, as you say, aren't
correlated anyway (except in one special and unusual case); but with the
additional vertical signal off the stylus. In mono>stereo>mono
de-clickers [1], it is the vertical component which is used to
distinguish noise from signal ....so any additional vertical signal has
the potential to compromise the operation of the device.

If the groove walls are traced out of phase [2], there will be a
significant HF component of the programme signal in the vertical
domain. This can false-trigger the channel switching/blanking circuits
*in phase with the signal*.

The results are horrible.



[1] Packburn, Mousetrap, Tuddenham, Garrard - but not Marantz.

[2] Or if they are traced with the correct geometry but were recorded
out of phase to start with.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Archived from groups: rec.audio.pro (More info?)

"Jim Gregory" <jim.greg@ntlworld.com> wrote in message
news:K6kke.1595$RG2.1111@newsfe6-gui.ntli.net...

> Thanks Arny.

Right now it seems to be kinda risky to mention numbers
around here, because one little mention of numbers and the
radical subjectivist police from #&!! start accusing you of
never ever listening. Nevertheless its quantification where
so many people go wrong. It seems like people mention can
mention some effect with no quantities attached to it, and
all of a sudden people are spending the big bucks to avoid
it. Some things matter, other things don't. A lot of the art
is knowing what matters the most and dealing with it.

> I knew it was really a trivial amount of error regarding
different
> "ploughed" distance and, as your maths have pinpointed the
accrued deviation
> for a 15-min vinyl side at 33.33rpm, I'm sort of relieved
& satisfied.

I'm glad to hear that my attempt to quantify of the effect
shed some light.

> "Arny Krueger" <arnyk@hotpop.com> wrote in message
> news:bYedncXAaqfFvgzfRVn-uQ@comcast.com...
> >
> > "Jim Gregory" <jim.greg@ntlworld.com> wrote in message
> > news:jnIje.8935$RJ6.956@newsfe1-win.ntli.net...
> >> On a conventional disc player, assuming its speed is
the
> > same as media
> >> disc-cutter....
> >> The tone arm (say 11" from pivot to stylus) is dragged
via
> > its stylus
> >> through an arc segment from outer groove to inner
groove
> > during its course
> >> of play. Ideally it should travel radially in a
straight
> > line as the master
> >> was cut that way - and it would track the usable
grooved
> > portion at a
> >> tangent.
> >> This delta alteration would generate tiny pitch
dopplers
> > related to the
> >> distance from the next-expected location of reference
per
> > rev. It passes
> >> through a maximum deviation and retreats again in a
> > curvature. Therefore,
> >> there are generally only two points where the stylus is
> > where it ought to be
> >> for those radii.
> >
> > Yes, because of this effect the stylus moves along the
> > groove about 1/2" out and in over the duration of a side
of
> > the LP.

> > In the same time, the stylus moves the length of the
groove.

> > In 15 minutes a stylus tracks something like 1200 feet
or
> > 14,400 inches. So this effect peaks out at something
like 7
> > thousands of a percent. IOW, its quite imperceptible.

> >> Is there a proper technical word for describing this
> > phenomenal parameter
> >> that arises from an all-too-frequent occurrence?

> > A trivial secondary effect.

> >>I have never seen discussed
> >> the altered-pitch aspect derived from the well-known
> > tracking error. It must
> >> be related to wow!

> > It has a very low frequency and a very very low
amplitude.

> >> Not to mention the angular errors that result in
slewing
> > from the true
> >> tangent.

> > That comes with a non-tangetial tracking tone arm.

I should add that non-tangential tone arms add quite a bit
of clearly audible FM distortion when there is anything like
deep bass in the LP recording. There's a Kilmanis/Rabinow
JAES paper about this. I've heard demos of the problem and
its for real. It's just that vinyl is so flawed that this is
usually lost in the noise and distoriton.

Archived from groups: rec.audio.pro (More info?)

Adrian Tuddenham <poppy.uk@ukonline.invalid.invalid> wrote:
>
>The problem is not with the clicks and pops, which, as you say, aren't
>correlated anyway (except in one special and unusual case); but with the
>additional vertical signal off the stylus. In mono>stereo>mono
>de-clickers [1], it is the vertical component which is used to
>distinguish noise from signal ....so any additional vertical signal has
>the potential to compromise the operation of the device.

Ahh! That makes sense! And, all of the spurious information is going
to be very high frequency which makes things worse.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."