Please read previous posts and what is being debated before jumping in the thread. I am now addressing absolute speed and the subjective effect of speed dragging when the arm is lowered. Not the instrument, but what people do with it.
Anyway what is the difference for a common user knowing he is listening at 33.32 in the morning and at 33.34 rpm next day? IMHO no one will notice it.
Then why measure at all? And why use a PC with spectral analysis software. Why make the statement that you find 33.30 to 33.36 to be satisfactory? If you are going to measure, why not do it as accurately as possible? Does anyone complain that their Fluke DVM is too accurate? Personally, I only look at the number of decimal places that are relevant to the task.
BTW masking will truncate not round.
Correct. Nobody said anything about rounding?
Surely your system can be used for diagnostics, and it was why I was asking more questions. But interpretation of data is not easy.
Fair enough. In my experience, static stylus drag (stylus down vs stylus up) shows up as a drop in speed of 0.01RPM or less. Without 3 places right of the decimal, this would be almost undetectable. The drag is almost entirely a function of belt creep, not slippage as you implied. Slippage can be cured with proper tension, creepage cannot. David's table uses a semi-rigid belt which suffers from much less belt creep than an elastic belt, so I doubt there would be any difference between stylus up vs stylus down, and if there was, it would occur at a much slower (inaudible) rate than with a lighter platter.
Dynamic drag is another story (change in speed with loud or dynamic passages vs soft). I'm not able to measure it even with 3 places right of the decimal, but in theory it exists. Even direct drive synchronous motor driven platters can suffer from this as the angle between the rotor and the magnetic field can vary with torque. The only reliable cure for this IMO, is platter mass; by definition, dynamic changes will be short lived, so the higher the inertia, the smaller the change in speed due to dynamic drag.
My point was simple since start - a good strobe with a quartz strobe flash light is all that is commonly needed to listen to vinyl. I am just thinking that most of our members consider that listening to their tapes is listening to their best source . Are they troubled by how accurate is the speed of their machines?
I don't know, are they? I'm not aware of any reliable way to measure it and if one exists, there's not much they could do about it if the speed was off.
I never read a complain of anyone claiming his CD player was playing slow or fast.
That's because the motors are servo-locked and the data is buffered, so playback speed is a function of the master clock, not a rotating disk. High end CD players use low phase noise oscillators to reduce jitter which can be measured (in the nano & picosecond range) and by most accounts, jitter does adversely affect sound quality.