Here's the original VPI HW-19 the sample TAS reviewed (I bought it from the reviewer) with MMT arm and Grado Reference cart. This data is tainted by the fact that the MAudio USB Duo was off by 0.6% at 44.1, this was also verified in the lab with calibrated reference equipment. I think I'm the only one that ever noticed.
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Great, looks plausible to me.
First question that begs is what f's are the apparent periodic contributions ?
It's straightforward to take an FFT of the display data series, to provide spectral composition. Bit-bucket spacing is then simply set by display repetition frequency, so one can readily calibrate frequency.......... amplitude I can't get my head around so I just left it to auto-scale, perhaps you can work it out?
LD
We can all work on it and you don't have to give away your tricks. The noise rejection of your technique is remarkable. For the problem at hand I do think we can get a lot of useful data with the simplified version. For the amplitude of the frequency components maybe dB re 1%? I don't know but referencing it against some standard of "goodness" might make sense. The 9Hz wobble on that VPI is pretty obvious.
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Thanks george as usual, but in this case do we really need to have two threads? The software tweaking is only of interest to a few and tuning up turntables is of interest to everyone. Most would just end up subscribing to both to not miss anything.
You pay service to the community. That’s highly appreciated, regardless of the number of the hard core members that will benefit from this.
We use all these 300Hz, 1KHz, 3kHz, 3150Hz test tracks to test the TTs rotational speed. We actually test it against what?
Having the recordings from many test records coming out from one turntable is a rare opportunity to find out the real nominal (and absolute) frequency of these tracks.
IMO it will be advantageous in terms of accessibility to find such posts easily whenever the need arises.
George
I agree, but before getting too excited....
.......one needs to establish that the rig used is healthy - so putting up a few files here so we can run polar plots seems a good precursor?
IIRC the rig at issue seemed worthy of sorting out a few issues before being considered for reference.......
LD
It's pretty unlikely that the detection method I came up with is novel, but it's possible so I'd rather not disclose. The Python library function, whatever method it uses, performs very well and far better than the standards when I tried them in this application. So that sort of reduces the chances that any of my tricks are worthy, I think. On the other hand, that's great news for wider use of this application, methinks.Yup, I have brain fade when it comes to mapping amplitude per Hz onto frequency deviation (Hz)............
LD
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Appols, my bad - I was confused and for some reason thought it was Davidsrb's rig to be used, which IIRC had issues.
I entirely agree the with you JP - the SP-10 MK3 and GAE would be fine, and hard to better.
Every encouragement and thank you - it would be well received.
LD
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I should note that we do have a thread on test records so I am happy to add any conclusions to that so there is a central reference.
In terms of 'turntable or test record' is there any value in recording a snipped, then rotating the record on the platter 1/4 turn and re-recording then repeat until you have 4 recordings. This should allow some inference of what is on the record and what is being added. A big pain but should only be required once per test record.
In terms of 'turntable or test record' is there any value in recording a snipped, then rotating the record on the platter 1/4 turn and re-recording then repeat until you have 4 recordings. This should allow some inference of what is on the record and what is being added. A big pain but should only be required once per test record.
Multiple captures only detect record vs turntable if you can get an absolute position on the record. This could be a defect on the record or by strobing the record during capture by the computer - something a Pi can do.
A dot of white paint on the edge of the record and an optical detector feeding the second stereo channel would also work for working out what zero degrees meant
I've had a think and I understand what I missed out saying. I was thinking of an interference fringe type situation, so the ripples will cancel and enhance depending on offset, but of course that won't tell us too much other than relative magnitudes, which might be enough. But a 'clicktrack' as s 3rd channel input triggered off a fixed point on the platter might add more information. I suspect most of us have bigger issues to fix before we get to this level, but worth consideration for enhancements.
Take the example of a trace that shows a 1.8Hz ellipse. This might be an offset hole or a bearing/spindle problem. Now rotate the record. The new trace still shows the ellipse, but without a reference tick from the platter or the record how do you tell which it was? The 12oclock of the polar plot is determined by the start of the capture file, nothing to do with physical
It was said that loose headshells or linkeages of tonearms and its interaction while playing test record made some variations in stability (I don't have ability to interpret that in polar plot) So will it be worth if while testing/recording test tone for speed stability we apply some artificial resonance (to plinth ? tonearm ? ) and simultaneously check the difference ?
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