Turntable speed accuracy

Atmasphere is quite correct about constant speed and soundstage.
There are many audible benefits with a turntable which does maintain constant unwavering speed which are unrelated to pitch.
With most turntables.......when the music becomes loud, and complex......the soundstage narrows and flattens, the transparency disappears and the sound becomes brittle.
This is caused by the auto modulation distortion of the soundwave in the time domain.
It is no different to a distortion in the amplitude of the soundwave which we simply would refuse to tolerate.
Those with tape decks have a better understanding of this phenomena and unfortunately........the majority of turntable listeners have not really experienced the liberation that accompanies constant speed control.
Once you do.......there's no going back:^)

" Musicians play things in certain keys and tempos for a reason" - Atmasphere

That's exactly right, and the point of my earlier comment. Deviation from the musicians' intent has a significant impact on the music. That's not to say that the music can't be enjoyed if there are small deviations, but there is no question that it's full impact can't be realized.

Atmasphere, I agree that speed stability affects sound staging. I also believe it affects perceived detail retrieval, and timbre. I use a straight
tracking arm (ET2), and I still hear improvements in staging when speed stability is good. When it is not, staging is not as defined and is slightly confused.

I think that in our attempt to arrive at a scientific explanation for all the perceived aspects of music playback, we overlook the very real possibility that there are many things that we don't yet fully understand; probably never will. As I said in an earlier post, time and rhythm are where the heart and soul of music lie. The subtleties of rhythm are extremely fine
and can be very elusive for the record/playback process. The relationship
between rhythm and timbre is likewise very important and difficult to understand. For example: experiments have been performed that show that the characteristic (individualistic) recorded tones produced by players on any given instrument are very difficult to tell apart if one removes the initial attack of a note, and listens only to the sound that happens after the attack. Speed instability alters the sound of the initial attack since the initial attack is connected to a point in time. With this in mind, it is not difficult to understand why speed instability can affect just about every aspect of sound.

 
"As I said in an earlier post, time and rhythm are where the heart and soul of music lie."

Nah. Rhythm without melody is heartless. :)

How accurate is the Timeline with its flashing laser?

supposedly time-base accuracy of 2 parts per million

Has that been measured for its accuracy ?

what happens when the batteries start to run down?

I heard about an audiophile living in Munich who usually proudly presents his very rare and expensive vintage items, including high calibre turntables. During a listening session someone stated "the sound is so slow, maybe we should check the speed accuracy". The result was 30,.. also being not very stable.

Speed was corrected to 33,33 and in the end the audiophile resisted listening to the correct speed sound. He said, I am used to the slower mode, it doesn`t matter if anything is correct. I love the sound!

Oh my god...

Best and fun only