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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?

128x128holmz

Showing 9 responses by cleeds

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cleeds
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holmz’s avatar

holmz

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 @lewm explains above, the stylus tip is always exactly where it needs to be.

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cleeds
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mijostyn
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."

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cleeds
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dover

... on a pivoted arm the stylus is advancing and retarding relative to tangent, therefore there must be a timing error ...

Your belief is easily disproved with a test record - it’s easy to measure the frequency of a test tone on an LP.

Fourier Transform, and all.

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cleeds
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holmz's avatar
holmz 
I am the OP, so it was my fantasy not @dover .

Oops, my apologies to @dover and 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.

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cleeds
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holmz
... 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.

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cleeds
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mijostyn

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.

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cleeds
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dover

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!

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cleeds
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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.

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cleeds
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lewm

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.

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