TT speed
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?
In plain English the issue is expressed in less than two lines. I think OP refers to the old potato that with a pivoted arm the stylus follow an arc across the disc whereas a parallel tracker follows a radius. As did the cutter across the master.
If this concerns him he should buy a parallel tracker like I have. |
@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." |
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). |
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. |
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.
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