Belt stretch

Rccc you can believe whatever you like but you should do so in the face of the available evidence:

1. Belt creep exists (see Mosin's post for one argument, there are several others)

2. I can measure it.

3. Doug Deacon can hear it.

Ketchup, if the lathe slowed down for a transient the recorded signal would rise in frequency. The playback would need to slow down by an equivalent amount to replicate the "original" signal.

The folks at Pristine Classical in the UK have extensive digital files of works which they have taken off disc and have performed analyses of the changes of frequency within sustained notes. They do this so they can find artefacts of the recording process and correct for them. From what I have seen there is no great effect attributable to the lathe slowing down under cutter drag.

I can think of two reasons why this might be: firstly, don't forget that the cutter head was heated and used on a relatively soft acetate formulation - very much like a hot knife through butter.

Secondly, modulation drag exists because the hysteresis of the cartridge suspension removes energy from the system, the larger the modulations the larger the energy lost. The only source of "make up" energy is the motor (everything else is passive).

The cutter on the other hand is actively driven so the larger the modulations the larger the amount of energy being put into the system. If the energy lost through frictional heating equals the energy inserted into the system we'd be in net balance.

Dougdeacon, great post!

I don't think you even need high quality equipment or perfect pitch to hear the effects under discussion. I owned a Well Tempered Record Player (belt drive), and now own a Technics SP-15 (direct drive) in the heavy Technics base. I definitely don't have perfect pitch, but I could easily tell the difference between the cheap stretchy 3rd party belt on the WTRP, the outrageously expensive precision ground flat plastic-like OEM belt, and the Technics, with the Technics easily besting the WTRP on all measures of speed stability. If you have better equipment, or ears like Dougdeacon's partner Paul, I'm sure the differences are both more readily apparent and probably really irritating.

Ketchup, as far as mastering goes, here's some interesting reading:

http://www.kabusa.com/1200agon.htm

Of course, the Technics wouldn't be factor for older recordings, which might very well exhibit the effect you postulate. These guys:

http://www.trutone.com/mastering.html

claim the Technics drive motors are way better the the original Neumann. I have no idea whether stylus drag was audible on the old lathes. Your theory has been discussed before here on Audiogon.

Anyway, I'm firmly in the camp that says belt stretch is audible, because I've heard it.

David

Reading the posts to date make me wonder if I am misinterpreting what is being argued.

It all seems very simple to me.

In your post you say that belt stretch is inaudible. In the next sentence however, you don't deny that it may produce measurable speed fluctuations.

In records that I am very familiar with, I can clearly hear differences of 1 or 2 rpm on a 33 1/3 rpm record. That's how I know when to change the belt on my table. And when I do change the belt, the records sound "right" again.

There are many turntables (or used to be) where you can adjust the rotational speed of the platter. I can remember sitting around college dorm rooms with my friends playing with turntable adjustments to see how the sound was altered. Adjusting speed was one of the things we used to do.

So I find that belt stretch, which in turn affects rotational speed, is easily audible. At what point it becomes audible, I don't know. But as I say, 1 or 2 rpm is certainly enough for me to hear a difference.

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