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Help me interpret this wow and flutter measurement for a cheap turntable

OK, here are the polar results for Marley vs Xerxes. They show speed variations against platter rotation angle for 3 rotations in each case. Note that the Xerxes polar (+/- percent speed) scale is different to the two Marley examples. Note also that one Marley example has spikes almost certaily due to clicks or pops on the LP.

http://jcgl.orpheusweb.co.uk/temp/MvsX.png
 
Interesting, thanks. So in both cases, but on the Marley especially obvious, you tend to get consistent per-rotation speed variation, I guess because of a platter not being perfectly round or a bearing not perfectly straight. Makes sense.

Tim
 
The basic 'once per rotation' variation can be because the center-hole of the LP isn't centered on the axis of rotation. That can be down to the LP having the hole off-center and/or the turntable spindle being off-center. More complex many-wobbles-per-turn can be problems with the bearings or motor drive. If the TT is belt drive, the platter ring is engages may be off center or not circular. Or the bearing resistance may vary. etc, etc. Can be a detective job to decide. The 'spectrum' of how much of the variation is once per turn, twice per turn, etc, can help diagnose. But the overall polar shape is useful as a guide as something like being off-center has a characteristic shape.

If the variations are irregular and not the same for every turn, its probably 'random noise', possibly due to poor condition or lubrication of the bearings.
 
Crusty old code still functions but needs a revisit. It's not clear to me at the moment whether the DSP approach offers any advantage overlooking for zero crossings. But at the time that wasn't the point, I had a book about DSP...

Looks similar enough to Jim's output to be comforting.

polar.png


There's a degree of hexagonality to the Xerxes, would be interesting to know if that's real. I was looking into plotting polars at different frequencies but didn't pursue it properly,
 
Paul R said:
Crusty old code still functions but needs a revisit. It's not clear to me at the moment whether the DSP approach offers any advantage overlooking for zero crossings. But at the time that wasn't the point, I had a book about DSP...

Looks similar enough to Jim's output to be comforting.

polar.png


There's a degree of hexagonality to the Xerxes, would be interesting to know if that's real. I was looking into plotting polars at different frequencies but didn't pursue it properly,
Click to expand...

I have wondered about plotting on a polar graph a set of points for the fundamental and amplitude for the 'offset' contributions of the first few harmonics of the rotation rate. Not tried it due to lack of 'round tuits' but it might clear some of the clutter of plotting as per my existing polar orbits.

The question of what's meant by 'instantaneous frequency' is an interesting one because there's more than one legitimate answer. :)
 
Jim Audiomisc said:
The basic 'once per rotation' variation can be because the center-hole of the LP isn't centered on the axis of rotation. That can be down to the LP having the hole off-center and/or the turntable spindle being off-center. More complex many-wobbles-per-turn can be problems with the bearings or motor drive. If the TT is belt drive, the platter ring is engages may be off center or not circular. Or the bearing resistance may vary. etc, etc. Can be a detective job to decide. The 'spectrum' of how much of the variation is once per turn, twice per turn, etc, can help diagnose. But the overall polar shape is useful as a guide as something like being off-center has a characteristic shape.

If the variations are irregular and not the same for every turn, its probably 'random noise', possibly due to poor condition or lubrication of the bearings.
Click to expand...

Well it will be never be perfect. Even the best-made and performing turntable, record, platter, bearing will have some imperfections. I'm very happy with the sound of the Xerxes, whereas with the cheap one I could tell it was slightly off; it's nice to have data to prove it.
 
I've run the Marley file through my Leader LFM-39A W&F meter and as I expected if you use the weighted JIS (RMS) standard it does meet its below 0.3% spec.
 
wd40addict said:
I've run the Marley file through my Leader LFM-39A W&F meter and as I expected if you use the weighted JIS (RMS) standard it does meet its below 0.3% spec.
Click to expand...

Thanks, a few questions:

- what is the RMS figure for the Marley?
- can you do this for the Xerxes and what it its RMS figure? Or let me know how to do this.
- given that "less than 0.3% RMS" is obviously a pretty poor spec, what spec should we look for as a minimum for reasonable performance?

Tim
 
Xerxes will be stunning judging by the visualiser results. I don't think you uploaded its file.

Ultimately results will be limited by how well centred the test record is.

Like so many other technical specs manufacturers often don't quote what standard their measuring to. If unstated it's probably safe to assume weighted RMS as this gives the lowest number...
 
wd40addict said:
Xerxes will be stunning judging by the visualiser results. I don't think you uploaded its file.

Ultimately results will be limited by how well centred the test record is.

Like so many other technical specs manufacturers often don't quote what standard their measuring to. If unstated it's probably safe to assume weighted RMS as this gives the lowest number...
Click to expand...

Thanks. Xerxes is in this file https://www.onlyconnect.co.uk/wowtests.zip Good point about the quality of the test record too.

Tim
 
A point I've made in the past is that the extent to which the LP is 'off center' can be measured by using *two* (or, preferrably, more) tone tracks at different diameters of the LP. The contribution due to off-center varies as 1/r. That caused by actual rotation rate variations stays much the same regardless of diameter. So multi-track measurements can let you distinguish.

That's one reason my programme should work with tones that are *not* the standard 3150/3000 Hz. It means you can use other tracks on a test LP that weren't designed for W&F. You just need a steady tone in the region from about 1k to 5k. It also means you can avoid a damaged track by using another on the LP.
 
Jim Audiomisc said:
A point I've made in the past is that the extent to which the LP is 'off center' can be measured by using *two* (or, preferrably, more) tone tracks at different diameters of the LP. The contribution due to off-center varies as 1/r. That caused by actual rotation rate variations stays much the same regardless of diameter. So multi-track measurements can let you distinguish.

That's one reason my programme should work with tones that are *not* the standard 3150/3000 Hz. It means you can use other tracks on a test LP that weren't designed for W&F. You just need a steady tone in the region from about 1k to 5k. It also means you can avoid a damaged track by using another on the LP.
Click to expand...

I thinks that these HiFi Sound test records that the OP used to test are notorious for being off centre. I have two copies and both are off centre you can easily hear it on the test tones without measuring.
 
RMS + Weighted the Marley roughly averages 0.2%, the Xerxes is approx 0.05% under the same conditions. Using the visualiser the Marley is roughly 2% pk-pk unweighted and the Xerxes 0.4%.

When using the meter there is a fair bit of pointer swing to be averaged by eye. I think the LP on the Xerxes is about as central as you're going to get it!
 
wd40addict said:
RMS + Weighted the Marley roughly averages 0.2%, the Xerxes is approx 0.05% under the same conditions. Using the visualiser the Marley is roughly 2% pk-pk unweighted and the Xerxes 0.4%.

When using the meter there is a fair bit of pointer swing to be averaged by eye. I think the LP on the Xerxes is about as central as you're going to get it!
Click to expand...

Brilliant, thanks. Agreed, it seems very well centred to me. Though a feature of the Xerxes is the removable spindle so you can do your own centering if needed!

Tim
 
I've now had a chance to work some more on the 'wow and flutter' program I wrote a while ago. It will now autogenerate a veusz file that can show and export output in this graphical form as a pdf, etc.

http://jcgl.orpheusweb.co.uk/temp/ATPLnew2.pdf

I'll need tidy up the code a bit so it is only as badly written as the earlier version. I'll then make the code available so Paul or anyone else who wishs can port it to Windows, etc. :)
 
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