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.
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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.
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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.
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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.
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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.
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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.
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Larry, You wrote, ...."at some point slowly moving forward (retarding, in terms of time), then at the top of the arc, it starts to retreat (speeding up)" 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.
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You are connecting two parameters that are not related. The stylus tip does not need to know where it is on the surface of the LP in order to reproduce the frequency accurately. It’s essentially a point in space.
For any pivoted tonearm, the stylus will describe an arc starting at the outermost grooves and swerving inward to the right of the spindle as it heads toward the lead-out grooves. When you use a typical 2-point protractor, like the Feickert, you can see this effect, because the protractor is helping you to locate the stylus and cantilever at each of the two null points defined by any of the 3 standard alignment algorithms. By definition, the stylus tip and cantilever should be parallel to the groove or perpendicular to the center of the spindle, at a null point. You have to rotate the protractor to set each of the two null points because the tonearm pivot defines one and only one arc upon which the null points have to be set. Please try to visualize that if my words are insufficient. Alignment can affect distortion characteristics, but it does NOT affect fundamental frequency. Because no matter where you are on the arc, the cartridge is reproducing what is encoded in the grooves at that point. When a test LP with a 1000Hz tone is created, it is done with a lathe that ideally automatically compensates for the changes in groove length (a spiral with an ever diminishing radius, heading toward the lead-out grooves). Your rotating the protractor is just to locate each of the two null points, has nothing at all to do with speed accuracy. So long as the platter maintains constant speed, 1000Hz is 1000Hz everywhere on the LP surface.
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Ditto to what testpilot said. I think you are saying that the two alignment points afforded by some types of protractors are typically separated by 20 degrees, using the arm wand and the pivot as the definers of the angle. But tone is about the constancy of turntable speed, not a factor much affected by alignment. The custom of checking alignment at two points is to improve the accuracy of the process vs just aligning to one point, which typically used to be the inner null point of a particular alignment algorithm. The classic Dennesen protractor used one alignment point, for example. Anyway, tone is speed. A 1000Hz tone recorded at the location of the inner null point will look different, if you could see it, from the same tone recorded at the outer one. So ideally the record cutting process accounts for the accuracy of the frequency, and then we need an ideal turntable with constant speed. Then you would hear 1000Hz at both locations on the surface of the LP.
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