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DIGIstrobo for Speed and Wow and Flutter Measurement, Thoughts? Experience? Competition? Dubious W&F Method?
Knowzy
post Jun 7 2010, 21:21
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DIGIstrobo: Clock Your Speed. Plus Calculate Your W&F?


Hello again.

I'm gearing up for round two of USB turntable sampling. This time I'm taking on USB DJ turntables. I planning to measure turntable speed, in addition to tracking force.

After some research, the only equipment I've found that fits bill is the DIGIstrobo from an Italian company called hifi4music. Positive Feedback has a nice review.

Does anyone have experience with this type of equipment? Are there similar "digi-tachs" I should consider?

I want to measure the speed out-of-the-box, not adjust it for the proper speed. That is why I'm not looking at traditional strobe discs.


Measures Wow and Flutter?
The manufacturer claims you can measure wow and flutter with it- something I would love to provide.

Here's how it works: While you're taking the speed reading, it keeps track of the lowest and highest speed recorded. Presumably, you arrive at a percentage based on largest deviation from the average speed.

The DIGIstrobo claims to be accurate to "0.05% (or 0.1 rpm)."

Clearly, this is a crude measurement but can you really arrive at even a crude WRMS or WTD figure through this method? Or is it really a speed variance measurement? The review uses the terms interchangeably.

The last time we discussed W&F measurement, I got the impression that the WRMS figure represents a deviation from a test tone, not a direct deviation from the measured speed.

If I come up with a percentage based on the DIGIstrobo method, do I even dare call W&F?
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Glenn Gundlach
post Jun 7 2010, 22:15
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Mainly tells you the hole is off-center on the disc. Please explain to me the fascination with vinyl because I don't get it. I heard my first CD in June of '82 and decided on the spot I wanted one. They weren't available until April 1 '83 which is the day I got mine and I haven't looked back - not once.

G

This post has been edited by greynol: Jun 7 2010, 22:27
Reason for edit: Removed unnecessary full quotation of the first post.
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Knowzy
post Jun 7 2010, 22:50
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QUOTE (Glenn Gundlach @ Jun 7 2010, 14:15) *
Mainly tells you the hole is off-center on the disc.

With all due respect, Glenn, that reply was not at all helpful. The function of the device is not in question, only its suitability.

QUOTE (Glenn Gundlach @ Jun 7 2010, 14:15) *
Please explain to me the fascination with vinyl because I don't get it.

If that's what you really want to talk about, why not start a new topic rather than hijacking this one?

Jeff
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DVDdoug
post Jun 7 2010, 23:40
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I don't think I'd trust that thing for wow & flutter. The review says something about a small disc and reflective tape. I don't know how any of that works, but I assume the reflective tape only gives you one measurement per revolution.

I understand that wow & flutter are a couple of basic measurements/specs for a turntable, but it's not something I ever worried about. I don't think I've ever heard flutter from a turntable, and I've only heard wow when there was something obviously wrong with a belt or drive wheel and the turntable was "dragging" (playing slow).

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Knowzy
post Jun 8 2010, 00:11
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QUOTE (DVDdoug @ Jun 7 2010, 15:40) *
The review says something about a small disc and reflective tape. I don't know how any of that works, but I assume the reflective tape only gives you one measurement per revolution.

That's right. They give you reflective tape that you stick on the platter or a record. The laser on the handheld device picks up the reflection once per revolution.

They also provide a disc about the size of a CD with a reflective stripe. However, using the reflective tape, you can test with a record and the needle down.

QUOTE (DVDdoug @ Jun 7 2010, 15:40) *
...it's not something I ever worried about. I don't think I've ever heard flutter from a turntable...

I can't argue with that. I guess I'm just obsessed with quantifying what makes one turntable is better than another. smile.gif
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Knowzy
post Jun 9 2010, 00:47
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I'm finding people who work with motors have been using these things all along.

Here's the Checkline CDT-1000HD for around the same price ($180). It has greater accuracy with +/-.02%.


Checkline CDT-1000HD. Click image for Data Sheet.



Then there's the one that I'm seriously considering: The Monarch PT99 ($200). Accuracy down to +/-.01% and tripod mountable so I don't need to worry about shaky hands affecting the results.


Monarch PT99. Click image for Manual.



Of course, neither of these come with a disc like the DIGIstrobo, just reflective tape. But I don't see myself using the disc anyway. I think that measuring with LP on the platter and needle dropped would be the way to go.

I definitely want to hear the HA community's thoughts on using this type of tool. I seem to be venturing into uncharted territory. I've only found two references to digital tachometers at the usual sources.

Jeff
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Glenn Gundlach
post Jun 9 2010, 04:30
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You are aware that a plain old strobe disc with a neon lamp or old style magnetic ballast fluorescent light will cost less and be more accurate than the digistrobo gadget. You can also get more accurate with a stopwatch just counting revolutions yourself. Of course it's not as much fun.

Unless something is totally messed up, 'wow' on a turntable is a 'once-around' of the platter and is usually a manufacturing defect of the disc -- the hole is off center. Flutter on a turntable is virtually non-existent. The mass of the platter damps out rapid speed changes. Flutter is more of an analog tape problem caused by the rapidly spinning capstan having imperfections or simply wearing out.

G
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Knowzy
post Jun 9 2010, 06:56
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Thanks. Now that's something I can use!

QUOTE (Glenn Gundlach @ Jun 8 2010, 20:30) *
You are aware that a plain old strobe disc with a neon lamp or old style magnetic ballast fluorescent light will cost less and be more accurate than the digistrobo gadget.


I'm ruling out a strobe disc because I'm looking to measure the speed of various turntables out-of-the-box. A strobe disc will only tell me when the platter is spinning at exactly right speed.

I suspect that some of these lousy USB turntables aren't quite at 33.3 and I'd like to report the exact speed I found them in my reviews.

I don't know of any other tools that can do the job.


QUOTE (Glenn Gundlach @ Jun 8 2010, 20:30) *
Unless something is totally messed up, 'wow' on a turntable is a 'once-around' of the platter and is usually a manufacturing defect of the disc -- the hole is off center.


Measuring wow and flutter would be a bonus. I've suggested another "poor man's" method in this forum. It was quickly shot down. I won't be shocked or disappointed if this one is too. smile.gif

The DIGIstrobo review suggested a W&F measurement was possible and he claims he was able to detect speed fluctuations in his VPI Super Scoutmaster.

The Audio-Technica AT-LP2D-USB lists its W&F at .25%. According to the method described in the review this means, over time, I should see readings in the range of 33.25 to 33.41.

I do realize that a bona fide W&F measurement isn't done by clocking the platter with a radar gun. I also realize that one sample every 2 seconds isn't a great deal of precision.

I'm just wondering if any useful data can come out of this exercise and do I call it a wow and flutter, speed variance or something else entirely.

Jeff
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WernerO
post Jun 9 2010, 11:11
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This thing is utterly useless for wow&flutter.

The spectrum of turntable w&f, once demodulated, is in the DC to ~200Hz band.

The digistrobe is a mere revolution counter. It gives average speed and, in the best
case, long-term drift. Not even remotely w&f.

If you are not interested in the drift figure, then counting 100 revolutions
against a chronometer is just as good.

If you are interested in w&f then you could use a test record with a known
reference tone, record it, demod it, plot spectrum. But beware, most
test records, and all present-day test records, are not good enough
for this.

For those who thing w&f is not an issue: the measured differences between, say, an SME30
and a Feikert or Origin Live are vast. After registering you can download a lot
of measurements at http://www.milleraudioresearch.com/avtech/index.html

Oh, and the PF review was written by someone who doesn't understand w&f ...


This post has been edited by WernerO: Jun 9 2010, 11:14
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Knowzy
post Jun 9 2010, 16:35
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QUOTE (WernerO @ Jun 9 2010, 03:11) *
This thing is utterly useless for wow&flutter... The PF review was written by someone who doesn't understand w&f.

That's the impression I'm getting. Oh well, I had to at least explore the possibility.


QUOTE (WernerO @ Jun 9 2010, 03:11) *
If you are interested in w&f then you could use a test record with a known reference tone, record it, demod it, plot spectrum.

I publish the W&F reference tone from the Ultimate Analogue Test LP right here on HA for every turntable I review. Even for the worst, ceramic cartridge USB turntables.

The problem is I don't have the software or know-how to extract a figure from it.

Thanks for chiming in. It looks like this type of instrument will really only serve as a way to measure speed. That is my primary goal anyway.
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Knowzy
post Jul 28 2010, 06:48
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I finally got a digital tachometer and tested the speed on all 5 USB turntables I own. No surprise: None of the $100 turntables spin at exactly 33.3 RPM.

I found a plethora of tachs around $40 on eBay with comparable specs to the DIGIstrobo and other models I mentioned.

I ended up going with this one, though I'd stay away from this seller unless you have a lot of patience. It took more than a month and a half for him to ship it from Hong Kong.

The Stanton measured dead-on at 33.3. Considering the platter has strobe dots and a light built-in, I'd be a bit shocked if it didn't. However, it was a good test of the tach's accuracy.

Here are the results for the rest of the turntables:
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Arnold B. Kruege...
post Jul 28 2010, 14:03
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QUOTE (Knowzy @ Jun 9 2010, 11:35) *
I publish the W&F reference tone from the Ultimate Analogue Test LP right here on HA for every turntable I review. Even for the worst, ceramic cartridge USB turntables.

The problem is I don't have the software or know-how to extract a figure from it.

Thanks for chiming in. It looks like this type of instrument will really only serve as a way to measure speed. That is my primary goal anyway.


Axon mentioned a tool he developed in his Blog. Have you tried it, or are we still waiting on him to publish it?
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Knowzy
post Jul 28 2010, 17:22
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QUOTE (Arnold B. Krueger @ Jul 28 2010, 06:03) *
Axon mentioned a tool he developed in his Blog. Have you tried it, or are we still waiting on him to publish it?

About a year and a half ago, we talked about his tool on HA and he talked about some preliminary results on his blog. I don't think he has published it yet, though.
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