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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?

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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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holmz OP
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@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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cleeds
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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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holmz OP
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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.

dover
2,254 posts
 

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 ?

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