Belt stretch

I dont doubt the theoretical possibility or even likelihood of differential belt tension what Im saying is that it isnt audible. I dont tune pianos but I do have perfect pitch and have spent much of my life in concert halls and enjoying Hi Fi. Its possible Mozart would have been able to hear those anomalies in a belt drive table, how many Mozarts are there on this forum? So let me rephrase what I stated. Aside from the esteemed genius's mentioned above no mortal can hear the effects of belt tension as has been reported in the audio forums and press. Why I started this thread is that knowledgeable people in the audio business have made reference to belt stretch,stylus drag etc but never quantifying it in any way but theoretical. I have both belt and direct drive and have never heard any speed related differences. Since this comes up from time to time I have asked freinds and associates in the music industry if they have and no one has been able to actually demonstrate the audibility of this variance. Im simply trying to debunk this myth or hear from someone whom can demonstrate that it is in fact audible to someone besides Mozart. I appreciate the thoughtful reponses but we have only addressed the possibility of some pitch shift not that it in fact exists and is audible.

Mosin, Im not arguing that belt slip exists or that rubber deforms or that there is some theoretical friction from stylus drag. Im questioning the audibility of these conditions and other than "I can hear it" and attributing "it" to the afore mentioned conditions no one yet has demonstrated that this so far unmeasurable speed variation is responsible for the effects they are hearing. If the speed measures stable with a strobe then what pitch related anomaly can be heard? When John hears better bass extension and dynamics with his idler compared to belt but both systems are showing no deviation in speed perhaps its not speed shift that he is hearing.

Im not saying there is no audible difference in sound between different systems or even belts. What Im saying is is that the audible difference isnt rpm related. Possibly coupling or who knows. Of couse you can hear if your tt is 1 or 2 rpm off, if it is it isnt working right and I have yet to see ( or hear ) a belt drive table that anyone on this forum would own that would be off that much. If stylus drag produces any speed anomolies that would be audible then Im saying that system needs to go in for repair. An example of what Im proposing is that the superiority of sound from an idler or rim drive which is being much discussed these days may have nothing to do with speed accuracy and be related to damping from the drive wheel instead. What I have yet to see is anyone demonstrating a hearing sensitivity of X to speed fluctuation and correlating that speed difference to a belt drive system.
ps: I knew I was going to be mugged when I started this post thanks for the great responses

Doug, I would love to do that thanks. Im hoping its understood that what I mean by belt stretch is that with a properly fitted belt in good condition the speed fluctuation as in the differential tensions discussed before would not be audible (except to Mozart) same with stylus drag. Mark is referring to a worn stretched belt (I think) which of course I agree would have an audible effect. One of the things I have observed is that on a turntable that has adjustable belt tension (like the one I built which can be seen over at vinyl nirvana) Changing belt tension makes no difference to measured speed stability until the belt is so slack it slips and surprisingly the loosest tension before slip yielded the best sound although the speed remained the same. This is actually what started me thinking about this in the first place. Thanks for your inputs

Geeze, I cant believe there's not one other belt slip skeptic out there. So you dont think that the idler sound may be attributable to something other than speed like say damping or ? I still havent heard anyone actually talk about a measured deviation in the belt system or if the speed is spot on wouldnt the differences in sound be due to something else or what resolution is audible (inaudible). What Im proposing is that the difference in sound may be due to some other forces. As I said before I could hear a difference in sound with different belt tensions while the speed remained stable. Although I follow the logic, bass extension and dynamics could be enhanced by other forces. Where the hell is HW when you need him?

"listen to a good quality belt drive table properly set up with a variety of belts. Hear the differences."
Doug, that is exactly my point. If the tt is properly set up and all youve done is change the belt and it strobes the same as the belt you had on before mabey your not hearing speed variation mabey what your hearing has something to do with coupling, damping or? With all the enthusiasm for the idler drive lately why assume the performance is solely (or at all) due to speed regulation since it seems these small deviations have yet to be measured or quantified or much less correlated to a paricular hearing sensitivity.
Thankyou for the fun dialogue Ill sum up by saying "if you dont know what it is you dont know what it isnt" and in that spirit Ill be researching this much farther and will report back on any ground breaking discoveries

John, you have offered no measurable explanation and per Ketchups post misinterpreted the data. If thats your version of logic I doubt we'd gree on anything. My mind is open to the possibility of these effects but I dont think enough testing has been done to prove the point. Ill concede Im very much a believer in blind listening and measurable performance. I do alot of comparative listening. Ill add that consumer audio is dominated by myth and conjecture as well as the magnitude of effects being grossly exaggerated. I think that kind of thinking does a disservice to the hobby at large and so when I hear performance claims being attributed to specific systems I want to know that they are on the right track. Does that sound logical?
Mosin, Thats a very good point. I think the core question is what amount of speed deviation is audible, how can it be measured and what are the effects (dynamics feq response image ect) I think its a question worth pursuing and will be experimenting with it in great depth. Thanks for your input.

Thanks Paul I was startin to get lonely.