When I use a protractor to align the stylus I do the alignment at the inside, and then rotate the platter maybe 20 degree when I move the arm to the outside of the LP, or protractor.
On a linear tracking “arm” it would not need to rotate at all.
At 33-1/3, then 15 minutes would be about 500 rotations. And that 20 degrees would be a delay of 18th of a rotation.
So a 1 kHz tone would be about 0.11 Hz below 1000.
It is not much, but seems kind of interesting... maybe?
but does put “another one” in the clip of the digital crowd’s ammo against analogue.
I have a friend who designs DAC’s way beyond what is available publicly.
His description of red book digital is "it is only a little bit out ALL of the time".
Without going into the weeds truncation errors due to the sine x/x calculation are built into the red book standards. Digital data transfer also contains errors in transmission - it is possible to fix these as each packet has a check digit, but you would need a Fugaku supercomputer to calculate the corrections in real time.
I have to credit Dover with causing me to re-think my prior position. He simply mentioned that the cutting lathe is linear and the tonearm is pivoted (assuming a pivoted tonearm). Rather than quantify the error, my simplistic approach is to start with the premise that the accuracy of the pitch (1000Hz) on this perfect LP being played on a perfectly speed stable TT depends upon the stylus remaining at a fixed point on the radius of the LP. That, of course, doesn't happen with a pivoted tonearm; it touches the radius only at each of the two null points, assuming proper alignment. When the stylus tip is off the radius, that represents relative movement of the stylus tip with respect to the recorded signal, which movement must change the pitch. Good thinking, Holmz. Interesting discussion, too.
Perform the demonstration in the last paragraph of my previous post. Keep the platter stationary and move the stylus from the outer groove to the inner groove area and measure the distance from the stylus to the tape when located at the inner groove. This is the linear distance the stylus will advance over the span of 15 minutes. At 60mm radius inner groove diameter, the circumference is 14.84". Divide the distance from the tape by 14.84 for the portion of the total circumference and multiply by 360 to give you degrees.
The fact the stylus is CW of the tape proves the length of the groove used for playback increases as the stylus travels towards the dead wax area. It's fairly easy to crunch the numbers and determine how much it advances on each rev. and therefore the change in pitch that will occur.
I thought this through over the last few days, and I agree, but I would explain it differently. I’ve done a 180, reversal of my prior opinion.There’s more than one path to the same conclusion. Still, I’d like to see a demonstration.
The OP is correct and his numbers are spot on target. The math to prove it is not difficult.
If the position of the cartridge changes by 20° from beginning to end of the LP, it will lengthen the time of the play back by 100mS: 20°/360°=1/18th of a rev; at exactly 33 1/3 RPM, 1 rev=1.8seconds x 1/18=100mS. The 100mS change in play back takes place over 500 revs (15 min) or 200µS/rev. So each and every revolution will experience a longer playback time of 200µS. 200µS/1.8S (expected time per rev @ 33 1/3)=0.00011111 or 0.0111% longer. Another way to look at it, the playback of each revolution will take 1.800200 seconds instead of 1.8S so the effective speed would be 33.3296 RPM (60Sec/1.80020). This will change a 1kHz tone to 999.888 Hz, assuming the record was cut with a linear tracking cutting head and the speed was held constant at 33 1/3 RPM.
The shift in frequency is insignificant and not audible even to someone with perfect pitch. It is not immeasurable or beyond calculation. It has nothing to do with tangency or FFT algorithms. It is purely a timing issue.
Another way to conceptualize this: Imagine a stylus is playing a 1kHz tone in a locked groove for 15 minutes (500 revs). Over the course of that time, the tone arm is moved in such a way that the tracking error stays within the expected range, but the stylus location finishes at a point that is 20° CW from its starting point in the locked groove. The effect would be the same as what is described by the OP.
My tonearm is 10" effective length. I placed a piece of masking tape on the platter to form a radial "spoke" on the platter. If I align the stylus tip with the tape at the outer groove radius (146mm) then rotate the arm to the inner groove radius (60mm), it is slightly more than 3/4" CW of the stationary spoke of tape. At 60 mm radius, 20° represents 0.824" of circumference. So a 20° shift in location is a reasonable amount.
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.
@cleedsI 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.
Oops, my apologies to @doverand you. That's a mistake I really try to avoid.
It is not “tangency”, but the walking of the point across the platter dues the arc of the tone arm.
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.
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.
Everywhere at any point on this LP, the 1000Hz test tone has been encoded by a perfect cutter lathe. In practice, the stylus tip is just a point on the surface of the LP; it doesn't "know" where it was a fraction of a second before or after any particular event. How can this phenomenon change the fundamental frequency?
The cutter lathe is moving in a straight line.
A pivoted arm is moving in an arc.
They are not congruent.
Does your direct drive turntable speed up and down to bridge the gap on each rotation ?
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.
if we change the speed of the patter we would alter the tone’s frequency.
Yes.
The tracking of a pivoting arm would look equivalent to linear motion of the overhang, moving slowly, in a linear tracker arm.
What you’re saying isn’t clear, but a properly installed pivoted pickup arm has a fixed overhang. Overhang isn’t affected by tangency - that’s fairly easy to measure. As @lewmexplains above, the stylus tip is always exactly where it needs to be.
@lewmI 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?
@cleedsif 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.
Everywhere at any point on this LP, the 1000Hz test tone has been encoded by a perfect cutter lathe. In practice, the stylus tip is just a point on the surface of the LP; it doesn’t "know" where it was a fraction of a second before or after any particular event. How can this phenomenon change the fundamental frequency?
Exactly, @lewm. And the answer is that it can’t change the frequency. We know that because the Fourier Transform proves why a little squiggly groove on an LP, or that same wave magnetically transferred to tape, or a binary digital code, can represent the sound of a full orchestra, and get the frequencies (pitch) correct.
What could affect frequency would be if somehow, on playback, the overhang changed. I can’t imagine how that could happen.
I just thought of a way one might test this idea. You would need the shortest pivoted tonearm possible with the greatest tracking angle error, since, I am thinking, TAE correlates with this movement forward and rearward with respect to the straight line radius of an LP. The more TAE, the more relative movement, the greater would be the frequency modulation. Among present day tonearms, I am thinking of the Viv Float 7-inch underhung tonearm. Underhung tonearms, which have zero headshell offset angle, inherently have much greater TAE than do conventional overhung tonearms with headshell offset. And for an underhung tonearm, the shorter the arm the more will be the TAE. So, if one could compare a linear tracker to a 7-inch Viv Float, on the same TT with the same test LP, one might be able to detect a difference in frequency stability.
We all get a bit snippy at times. I'd rather ignore that and get on with this somewhat interesting discussion. (At least it beats talking about what phono stage a stranger should buy.)
Dover, I respect your knowledge, and I certainly agree with your thesis about what the stylus tip is doing with respect to the two null points. But the movement you describe is not happening on a stationary LP; it's happening on an LP moving past the stylus tip at 33.33 rpm (ideally). Everywhere at any point on this LP, the 1000Hz test tone has been encoded by a perfect cutter lathe. In practice, the stylus tip is just a point on the surface of the LP; it doesn't "know" where it was a fraction of a second before or after any particular event. How can this phenomenon change the fundamental frequency? The analogy about moving a 15-foot auto 10 feet and then thinking about how that affects its length is not a bad one for making the argument that there is no effect. This is definitely not the same as a DJ doing "scratching", which I think holmz said is what inspired him.
If you and the others are thinking that tangency to the groove per se and lack of tangency in between or before or after either null point is altering frequency, that I can understand, but I don't think that would alter the fundamental tone of 1000Hz; what it probably does do, where there is lack of tangency, is to produce distortions. Harmonic distortion would produce some frequencies that are multiples of 1000Hz, and other forms of distortion would produce odd frequencies, but the 1000Hz signal is still there. I am guessing you know this.
It’s interesting how some people think math is intuitive, and that they’d rather pursue a fantasy than understand what is really basic math. What’s odd is that they’ll resort to such personal attacks and invective in defense of a fantasy, while attacking those who understand the underlying science. But this is a hobbyist’s group, not a scientific forum, so I guess that’s to be expected from time to time.
The only thing unusual in this instance is the ease with which the claim that tangency affects frequency can be disproved.
Assuming the record is travelling at constant speed, then the motion of the stylus forward and back relative to the line must alter the apparent speed, as seen from the record groove, albeit minuscule.
You are really confused.
Your fervour for FFT analysis appears to be an impediment to understanding basic maths and physics.
You are really confused. I’ve never, ever mention FFT analysis. You’re apparently confusing FFT analysis with the Fourier Transform, an indicator that you’re having issues with your "basic maths."
The Fourier Transform is the theorem which explains how digital and analog audio work. It also disproves your fantasy that phono cartridge tangency affects frequency. As I’ve mentioned, I can also disprove your fantasy by measuring the frequency of a test tone as it’s played from a test record. It’s not difficult to do.
Of course, you’re free to imagine and fantasize that you’ve found some flaw in the Fourier Transform. A Nobel Prize awaits you if you can show you calculations. Good luck with that!
Your belief is easily disproved with a test record - it’s easy to measure the frequency of a test tone on an LP.
We've already shown that measurements reveal it doesn't exist. It's easy to measure a 1 kHz tone on a test record.
Unfortunately you can't see the wood for the trees.
If you draw a line across the 2 null points of a pivoted arm, and are using Baerwald for example, then at the beginning of the record the stylus is behind the line, as it crosses the first null point it will move ahead of the line, and then as you cross the second null point it will fall behind the line.
Assuming the record is travelling at constant speed, then the motion of the stylus forward and back relative to the line must alter the apparent speed, as seen from the record groove, albeit minuscule.
Your fervour for FFT analysis appears to be an impediment to understanding basic maths and physics.
@lewmI 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.
Holmz, if you are thinking of how to prove or disprove your frequency hypothesis, I fear we cannot do the experiment in the real world, because we require a perfectly created, perfectly centered, and perfectly flat LP on a TT with perfect speed accuracy, in order to examine the phenomenon you claim exists (and others do too, in fairness). Imperfections in any of the foregoing elements would likely cause a frequency distortion that would drown out the effect you want to detect. Fourier or no Fourier. But we can argue until the cows come home.
By the way, I was thinking that your observation, that you have to rotate the platter by about 20 degrees in order to set the two null points using your protractor, is really a product of how your particular protractor was made. It is possible to imagine another protractor where the cartridge can be aligned at the inner and outer null points without having to rotate the platter at all.
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.
Theoretically pitch is affected but the effect is so slight that it may well be unmeasurable.
We've already shown that measurements reveal it doesn't exist. It's easy to measure a 1 kHz tone on a test record.
... the turntable spins at a constant speed. As the arm travels in to the center of the record the radius that the stylus is on shifts clockwise, this is what I an calling translocation (I think I borrowed a medical term). This slows the speed of the groove by the stylus ever so slightly lowering pitch. This would probably never be measurable never mind noticeable but, it is real. It is not as professor cleeds says, "zero."
Well, "Doctor" Mijostyn, you'll have to show your math that disproves the Fourier Transform, because that's the math that shows how an an LP - and digital for that matter - work. Fourier is not a theory - it's proven math, so that should keep you pretty busy, perhaps for the rest of your life.
The .11Hz change in pitch is WAY off the mark--that was calculated by looking at the angular difference at its extreme, which are many minutes apart, then calculating what this angular change means in terms of pitch. But, say the recording is of a 1,000 hz signal, at any point along the record, it is playing a 1,000 hz signal, which is what you would hear no matter where on the record, you are playing. To the extent the very tiny movement forward or backwards from the movement of the tonearm along an arced path changes pitch, it is extraordinarily small, and the amount of movement is dependent on the time frame one uses to measure the change. If one measures say a two second interval, there will be an extremely small change in position relative to the starting position, which, I suppose, could represent a theoretical pitch change; a one second interval would then be about half as much of a change, and .5 sec, half again (kind of a Zeno's paradox). The instantaneous pitch (if there can ever be such) would respresent a point with no change at all.
The fallacy of comparing the two extreme points on the record and calculating the difference as a change in pitch, is somewhat like the following analogy: Suppose I have a fifteen foot long car. If I move it ten feet forward, what I have after the move is a fifteen foot car whose location is 10 feet different from where it originally was located. It is not a stretched out 25 foot car covering the interval of its movement (again a problem Zeno grappled with).
@cleeds, nice to have you back again cleeds. Theoretically pitch is affected but the effect is so slight that it may well be unmeasurable.
@lewm, the turntable spins at a constant speed. As the arm travels in to the center of the record the radius that the stylus is on shifts clockwise, this is what I an calling translocation (I think I borrowed a medical term). This slows the speed of the groove by the stylus ever so slightly lowering pitch. This would probably never be measurable never mind noticeable but, it is real. It is not as professor cleeds says, "zero."
I know, it is a small number, but just the thought made my brain explode. I doubt that I will understand it. This course of logic doesn't come easily to me, and so that may be the reason it fascinates me.
The things that we may never understand (speaking for myself really) don't defy observation of occurrence, just maybe the ability to understand.
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.
It still twists my mind, but I enjoy the talk. Thanks. It is almost like an original thought for me that now will be a challenge to analyze.
I see different perspectives here that don't jive. One aspect can be true from a certain perspective, but to change the perspective may be not to disprove the first, as it may seem. The second perspective may not be in line with the subject as was first supposed.
Then there are of course those who chime in with what seems to be relevant but is not.
Just thinking out loud here. Appreciate the thread.
... 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.
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 had pitch problems with my VPI Hw-19, with a linear tracker (Clearaudio Triquarz) as well as a pivot arm (SME V). Now, with a Hanss T30, with a superior dual motor / 6 string system, I don't have them.
Assuming a perfect test record, you could playback a pure 1kHz tone from the beginning of the LP to the end. Any deviation would be the result of the turntable’s w&f, not any "translocation of the stylus."
That statement is not correct.
Holmz is correct - on a pivoted arm the stylus is advancing and retarding relative to tangent, therefore there must be a timing error, but it will be minuscule on rotation re adjacent grooves.
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.
The translocation of the stylus is so slow that it’s effect on pitch is insignificant.
Assuming a perfect record (absolutely flat, hole exactly in the center), the "translocation of the stylus" will have zero affect on pitch. Zero.
Assuming a perfect test record, you could playback a pure 1kHz tone from the beginning of the LP to the end. Any deviation would be the result of the turntable’s w&f, not any "translocation of the stylus."
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.
@holmz, I understand what you are saying. The translocation of the stylus is so slow that it's effect on pitch is insignificant. Warps in the record surface and eccentricity of the spindle hole are far more significant in terms of pitch irregularity.
Thanks @4krowmeit 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.
OP, Though I couldn't get what you were describing, it finally came clear when larryi posted. Whether it matters or not, it still is something that I had never considered before. A new thought for me. I very much appreciate discussing or learning about these sorts of topics.
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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