Stylus-Drag..Fact or Fiction?

Dear friends: I would like to know if each single LP was recorded/cutted at exactly/accurated 33.333..rpm and if for any reasons exist tiny deviations from 33.333..rpm accuracy why or how can we or not detected through an accurate TT that spins at exactly 33.333...rpm during play time of LPs? 

I think that some one can put some light about.

 The stylus-drag is a fact and can be fixed but those tiny differences in speed/pitch always comes by speed non-accurated TTs or by the LP it self?

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

Phoenix, Thank you for embellishing on my response to Atma-sphere re my point that operating a motor with 3-phase AC synchronicity does not per se eliminate cogging.  I am a rank amateur on this subject with only a good college level background in physics (and a lifelong habit of thinking like a scientist).  But I was a bit puzzled by your statement: "A 24 pole motor turns at half the speed of 12 pole motor so the frequency of the cogs is identical in both (120Hz)."  In a direct-drive turntable, doesn't the motor have to turn at 33.3333 rpm, regardless of the number of poles?  And therefore might there not be a theoretical advantage to having double the number of poles?

Oh, and thanks for clearing up the many ambiguous on-line websites that don't come right out and say that coreless motors are free of cogging.  It makes perfect sense (and I think I hear the benefits), but you'd be surprised at how poorly this subject is addressed and explained. (Or maybe you wouldn't be surprised.)

Raul raises a good point. How accurately are the various cutting lathes spinning? This is a whole different topic. 

It does lead nicely into long term average speed accuracy....
There is a trend to show how incredibly accurate peoples DD TTs run, posting videos using the timeline over extended runs. This is a great demonstration of how accurately a TT's long term speed control can be.

But how important is an average 33.3333333 rpm?
Lets say TT1 runs at an average 33.333 and TT2 runs at an average 33.334. A 1000hz tone cut accurately at 33.333 would of course be played back at 1000hz on TT1, but it would be higher on TT2 at 1000.03hz.
I don't claim to be able to hear this difference. 

What I think is important is the TTs dynamic speed accuracy. How does it behave under a varying load. I believe that we are sensitive to real time changes in pitch. But do not hear them as such. Halcro describes the Raven as being more relaxed than the Victor. This general description pretty much covers many BD/DD comparisons. Clearly we are hearing differences but not describing these in terms of pitch. We  use different descriptors.. 

The timeline only tells us how long it takes for the platter to make one rotation. Confirming, or not, that it took 1.8 seconds at its 33.33 setting. That is, was its average speed 33.33 or not.  It does not tell us anything about what happened to the platters dynamic speed during that rotation. 

Yeah, yeah, the platters inertia will save you, I don't think so. There are no free lunches.  


Chris.

Many thanks for the input of which I completely concur.


Lewm
I couldn't resist!  

Dear @richardkrebs  :  "   This is a whole different topic. ", yes diferent but with direct relationship with " audible "/or not speed deviations that we " charge  " to the TT culprit when maybe not always came from the speed unstability in the TT.

Perhaps we need a recording engineering to answer the question, that I remember in this moment Atmasphere has enough experience about and maybe he could chime here on it.

In the other side:  "  TTs dynamic speed accuracy. """ M.Lavigne posted about " steady " as the critical issue and yes this is the main subject with any TT.

In your example if both TTs are " steady " we can't be able to detect it and maybe we can't even if not steady because speed difference is so tiny.

R.

"But I was a bit puzzled by your statement: "A 24 pole motor turns at half the speed of 12 pole motor so the frequency of the cogs is identical in both (120Hz)." In a direct-drive turntable, doesn't the motor have to turn at 33.3333 rpm, regardless of the number of poles? And therefore might there not be a theoretical advantage to having double the number of poles?"

My statement was in response to the assertion that adding more poles reduces cogging (it doesn't).  Doubling the number of poles does not change the vibration signature because it will also cause the motor to turn at half the speed (assuming the same 60Hz drive signal).  Both a 12 pole and a 24 pole motor will produce vibration from cogging at 120Hz (10 revs/sec x 12 poles at 600 RPM  and 5 revs/sec x 24 poles at 300 RPM).  The amplitude of the vibrations is directly proportional to the power consumption of the motor, not the number of poles.  If you go to the link I provided, you will see that the measurements bore this out.

The motor on a direct drive table does turn at 33.333 RPM so the number of poles will determine the drive frequency needed in that case (RPM=Freq x 60/pole pairs or Freq=RPM x pole pairs/60).  If the motor uses steel pole pieces, it is subject to cogging and the frequency of vibration will be 0.555Hz x number of poles;  in most cases, this would be below 20 Hz so it will show up as rumble.  To run a DD motor from 60Hz would require 216 poles.


From what I've seen, most of the DD tables use a DC motor with servo control (feedback) to maintain proper speed.  This of course, comes with its own set of problems.