TT speed

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.

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.

@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.

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.