Turnable database with TimeLine

Hi Lewm,
How can micro variations in speed due to groove modulations be measureed with a laser light that flashes just once every 1.8 seconds? The answer is that it cannot. The Timline gives you average speed- that's it. Don't try to read into it anymore than that. Sure, you can see the difference in average speed for an unloaded platter vs. a platter with stylus load; but you cannot measure the micro variations in speed with an averaging device. It must be an instantaneous device like a tachometer. The Timeline is a nice little package that has laboratory grade accuracy for a realatively low cost. A Tachometer with equivalent precision will cost significantly more, I'm sure. The danger is mis-using the data from an averaging device. For exmaple, the speed error for variable stylus drag is cumulative. So the longer you play the record and measure speed, the more the average, in percent, will deviate from 33 1/3. (If the stylus drag is constant, then the error will not accumulate- ie. the average speed will remain a constant delta in percent from 33 1/3). See, things can get murky real fast when working with averages. You can infer stylus drag is causing variations in platter speed with the Timeline, but actual measurements are not possible.
Back to my car analogy: Try driving and maintaining speed with the Average Speed readout on your car's trip computer. Once you have accumulated a couple of miles on the average speed computer, the speed reading will not change much even if you go very slow or 120 mph. The police officer is using an instantaneous speed readout device. Good luck convincing him not to ticket you because your average speed was below the limit. (If that does work, let me know how you did it!)

Tony, According to others, the laser flashes 6 times per revolution. That means you can get a read-out every 0.3 seconds. So you are indeed "averaging" the speed, but it is over a very small increment of time. Your talk of a "tachometer" is specious. Tell me what you have in mind more precisely, because when you use that term I envision a device that must be mechanically linked to the platter. Any such device will be subject to errors caused by tolerances in the mechanical linkage. There is always slop in any mechanical linkage. Also, any mechanical linkage cannot help but also have an effect on the performance of the turntable, the Heisenberg principle. If you chop up time into increasingly tiny aliquots, you approach a continuous read-out. By the same token, the readout can never be truly "instantaneous", nor can that of a tachometer. The Timeline does not get there either, but it gets very close. Which is why I asked aloud about the time required for servo responses in a high quality dd turntable. The comparison to a car computer is pointless, not a good analogy at all, IMO.

The odd thing is that I don't own a Timeline and never plan to own one. I choose my tt's based on how they sound and if they can hold speed with a KAB strobe. If the "33" on the strobe disc does not wiggle, much less move at all, I am happy enough. Then I listen.

I'm not sure it has been confirmed that the newer Timeline devices have 6 flashes per rev. At least the ones everyone is using seems to have just one flash per rev. Regarding tachometers: most today and even the one in your car uses either optical or hall effect sensing devices. They are not mechanically linked. The accuracy is dependent upon the precision of the encoder ring. Good data capture for micro variations in speed would need to be in the 40kHz range (two times max frequency response of a record), at least. That is several orders of magnitude beyond even 0.3 seconds.

Since the timeline is equipped with only a single laser, it can only produce one reference point per revolution that can be measured against any subsequent revolution. If you want to increase the sample rate, you would need 6 separate lasers flashing once every 0.03 seconds; not a single laser flashing 6x per revolution.

Tony and Brf, I hate to be wrong, but I see your point(s). I saw Brf's point in my own mind, shortly after my last post. Most servo-controlled DD turntables have some sort of platter speed sensor, optical or otherwise. One could probably tap into the output of that data stream to get a continuous read-out of speed stability. That may be what Denon did in order to produce the figure shown in their ad copy for the DP80, which I described above.

Henry, I don't think Syntax's post about the Kuzma was so provocative. As I noted, the fact that the Kuzma was a little fast (or slow; I cannot recall) is not so important as whether it was stable in speed, because a decent motor controller could probably bring it back to exact constant speed, if the error was also constant. But he never responded to my question in that regard. I am not a "Kuzma guy", but I would imagine they have a recommended motor controller for their better models, such as the Reference.