@lewm I mentioned the scratching more as humour, but that is also the motion needed in the wrist if we put a spoke onto the record and help the stylus tip on it as the move from outside to inside.
I already gave the method for a relative test using a linear tracker and pivoted arm earlier. And an estimate of 0.11 Hz offset at 1kHz.
A relative measurement removes the platter speed and W&F from the equation.
But where does one get an LP with a tone on one side? If there a link?
@cleeds if we change the speed of the patter we would alter the tone’s frequency.
The tracking of a pivoting arm would look equivalent to linear motion of the overhang, moving slowly, in a linear tracker arm.
albeit, it is close to zero.
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I am sure it doesn’t matter, but unless the track is running in a circle, the pivoting arm will produce a very slight chirp in the tone.
The example of a linear tracker with a moving overhang is obviously not something that one buys… but it was yet another example to convey the effect of what is happening with the arm, that makes the platter look like it is advancing or retarding as the arm moves inwards.
What was an “ah ha” moment for me, was obviously not shared well or described too clearly.
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I am the OP, so it was my fantasy not @dover .
It is not “tangency”, but the walking of the point across the platter dues the arc of the tone arm.
But as was pointed out in the very opening post it amounts to “a bee’s phallus” amount of shift… I used the term, “it is not much”.
(Where “Bee’s _ick” is the Australian slang term for “a small and almost immeasurable amount”. I believe that the UK uses the acronym of “SFA”.)
My main claim was that I found it “somewhat interesting”.
What is more interesting now, is that we do not agree whether it is truely happening, or just a fantasy.
And also that my communication likely uses a lot of body language and hand motion to describe physical things.
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Sorry, you will need to restate your question as I don"t have a clue what you are asking. Also, state the type of protractor, single point, arc etc.
@testpilot It is a paper protector for a 9” arm which has 13mm of overhang. Maybe Baerwald? I don’t know for sure.
@lewm I am saying that when aI go from the outside to the inside, I need to rotate the platter somewhat… maybe 20 degrees, but probably less.
So I am saying that the arm moves in a way that makes it advance or retard with respect to the platter spreed. I need to remove some rotation the platter more going from the inside to the outside. (Add rotation if going form outside to inside)
The stylus is not moving linearly along a fixed line radially inwards. It is moving in an arc that is not perpendicular to the track’s direction.
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At least it is not a large number, but maybe it accounts for a tiny perception of tonality in people with pitch perfect hearing?
(Not me)
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Thanks @4krowme it was great that Larry could describe it better.
I felt like a scratch DJ moving the platter back-n-forth over the protractor when it occurred to me.
So it is more of interesting… but not entirely relevant.
If we had a short recording where the tracks were widely spaced, then the error gets bigger than say a super long “LP” record with more tracks being closely spaced.
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I suppose that since the speed variation from the stylus movement angle is lower than most W&F specs it is not really a concern.
I think that what he is saying is that the stylus tracks an arc across the record, which means it is at some point slowly moving forward (retarding, in terms of time), then at the top of the arc, it starts to retreat (speeding up). Both the slowing of time and the speeding up covers the entire side of the record and covers such a small number of degrees of arc (hence small fraction of one cycle of the record) that it has nothing to do with what can be perceived in terms of pitch change or timing.
^Well put^ sir, that is exactly what I was trying to say.
I think you would agree that although the velocity of the stylus tip does decrease as it moves from the outer grooves toward the inner grooves, just because path length is getting progressively shorter per revolution of the platter, this has zero effect on pitch, assuming a perfectly created test LP and a turntable with perfectly constant speed.
The fact that the cartridge moves some number of degrees of platter rotation, effectively would be the same as running the platter bit faster or slower… assume that the patter was, say, perfect in its speed,
The fact that the platter speed variation is greater than this Mathematical tracing delta makes it somewhat a moot point.
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What? To be clear, I am questioning what seems to underlie Holmz’ thesis. Maybe I could understand if you (Holmz) were to define the "top"of the arc, just for starters. But I still cannot agree that pitch errors are caused by or related to the position of the stylus tip on the LP surface, again given a perfect recording on a turntable with perfect speed control. I would also ask Mijostyn to say what is meant by "translocation" of the stylus. I seem to be missing something.
Let’s say that the top of the arc is the outside edge of the LP, and the bottom is the spindle side.
- Assume that the platter would spin at exactly 33-1/3.
- When I put a protractor on it and start at the outside, and then move to the inside, I need to rotate the platter to get the stylus on the arc.
- so the stylus goes backward and would end up behind the spindle
- However with a linear tracking air bearing arm, I do not have to rotate the platter at all, and it’s protractor is a straight line.
- It runs straight towards the spindle
- zero angular platter change.
If I play the LP with both the regular arm, and also with the air bearing linear tracker arm, where does that required rotation of the platter end up? The rotation needed to get stylus onto the protractor?
Those two arm styles are not the same in terms of angular platter change.
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@cleeds the error would need to be less than the W&F “noise”, and my stab at the error would be about 0.11 Hz at 1 lHz.
So it is likely to be more of an intellectual oddity than a severe problem.
Mathematically though. I believe that a linear tracker and pivoting arm would produce very slightly differing pitches.
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You're arguing that tangency affects pitch? If so, that violates the Fourier Transform. That's not possible and, as I mentioned, also easily disproved with a test record.
I would rather use the term orthogonal or radial over “tangency”.
The stylus in the linear tracker runs straight along the radial spoke towards the spindle.
But let’s suppose that we set up the linear tracker to be at, say, a 45 degree angle and adjusted the alignment so that cartridge was derotated by the 45 degrees to be exactly tangent to the track (which is an absurdity with a curved sound track - unless it was maybe a curved “linear” tracker…).
It should be easy to see in that case, that as the linear tracker moves inwards that with each rotation and the stylus moving towards the spindle, that it gains or looses a a bit of angular platter motion because it is displaces off of the radial spoke.
In the end it has gained or lost 45 degrees of platter rotation between the beginning and and of the LP.
Then there are of course those who chime in with what seems to be relevant but is not.
Me perhaps? 😀
it is a small number, so its is not likely relevant…
It just got me doing an Ah-ha with a chin-scratch, beard-stroking and the pate-rubbing.
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Personally I would not use an FFT for fine measurements.
A better method would be shift the 1kHz down to DC and then plot the phase as a function of time.
The width of the FFT bins will mate it appear like it is one frequency, but it will be a chirp in frequency,. And with any spindle hole offset, it will be a chirp with with a sine wave riding on top of it.
There will no now way to get the sample rate high enough to have the FFT size be high enough to get any sub Hz resolution.
And with the chirp and sinewave it will be smeared within the bin to all buggery.
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@lewm I agree it is somewhat meaningless in term of the platter speed and W&F levels…
But ignore the protractor and just draw a radial spoke on the paper. And there too… as the stylus moves inwards walk in “platter rotation space”… (well all except a linear tracker)
We do not need to do an experiment, as we can do it all solely with trigonometry.
(I might write a program to show it.)
However for an experiment we could do it with a two arm table if one of the arms was a LT. Then we would time align at the start… or we would just do a cross correlation every so often to show the offset as a function of time, which is the time delay as a function of platter position.
This method (being a relative measurement) would remove all the W&F and platter speed, but still probably includes some effect from the offset holes.
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Your fervour for FFT analysis appears to be an impediment to understanding basic maths and physics.
- The FFT is pretty much sub-optimal for anything but gross frequency related analysis.
- There is the cross correlation (time domain) - which requires some known signal to compare the measurement to.
- Or there is direct phase, which is superior to FFT analysis.
- Phase is the derivative/integral of the frequency
- So the rate of change of the phase give us the frequency much more accurately than super long FFTs to achieve small FFT bin width.
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Thanks for the clearer explanation @phoenixengr
It is indeed a SFA* amount of shift.
* SFA is a UK/Au expanding to “Sweet F__ All”, which generally means is to the point of not mattering.
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I’ve done a 180, reversal of my prior opinion.
Real or imaginary part?
I have to credit Dover with causing me to re-think my prior position.
Thanks @lewm It looks like we can credit @larryi , @dover and others for helping me explain it properly. Many thanks fellows.
At first I was “… like… WTF.”
But then the math resulted in, “<and>… like… who cares…”
It is prolly just of minor intellectual curiosity, but does put “another one” in the clip of the digital crowd’s ammo against analogue. 😋
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What you’re describing is tangency, I don’t know why you’re not comfortable with the word commonly used to describe this aspect of pickup arm geometry. Tangency has zero effect on freqeuncy (pitch). But I’m done with this conversation - the question you’ve raised is easily answered several ways, as I’ve already pointed out.
@cleeds I am not comfortable with the word, because
- It is the wrong word.
- Tangency does not affect pitch.
According to audio technical what we are talking about is not tangency:
The term “translocation” was used earlier, and that at least is not able to be easily confused with the stylus being parallel to the track, or tangent with the track… which is what “tangency” commonly refers to.
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