@Jan.Didden,
Well, I started this subject to show everyone the deviation by eccentricity. Because when I tune a music instrument I never will accept the difference in frequency between the real tone – for example the A (440 Hz) – and the A from the record that’s going every 1,8 second to and fro between 438,7 Hz and 441,3 Hz (0,2 mm eccentricity). Nevertheless, the human brain likes the sound of vibrating tones...
Well, I started this subject to show everyone the deviation by eccentricity. Because when I tune a music instrument I never will accept the difference in frequency between the real tone – for example the A (440 Hz) – and the A from the record that’s going every 1,8 second to and fro between 438,7 Hz and 441,3 Hz (0,2 mm eccentricity). Nevertheless, the human brain likes the sound of vibrating tones...
@billshurv,
I am trying to develop some low cost applications that will improve the quality of the music from vinyl records. Not for myself, but for everyone. If it was only for myself I didn't spoil my time by visiting forums.
I am trying to develop some low cost applications that will improve the quality of the music from vinyl records. Not for myself, but for everyone. If it was only for myself I didn't spoil my time by visiting forums.
I admire you goal, but the target market for this will be very limited. You have to assume you are doing this only for yourself.
I have modified my tonearm for measuring eccentricity (photo below). Now the distance between fixed pivot and the tip of the fixed stylus is 16 cm instead of 9 inch (22,86 cm). The distance between wall and fixed pivot is 1,6 m, so the magnification is 10 times (0,1 mm eccentricity is 1 mm at the graduated scale). The clothespin is because of the push button of the laser pen (5 euro).
The average 12 inch record has an eccentricity of 0,3 mm (classical music records about 0,2 mm). The eccentricity of the record at Youtube is 0,6 mm, so the horizontal to and fro movement is clearly visible.
I have centred one record by hand – the centre hole of this new record is far too wide – and the result is an eccentricity less than 0,02 mm (the red laser dot is only moving up and down). The distance between the fixed pivot and the wall was 3,2 m.
After all, I am not satisfied about the result (the laser tonearm). Because I have to walk between the graduated scale and the platter to adjust the eccentricity. Therefore, I will shorten the tonearm even further to 10 cm. So the fixed pivot has to be above the record (the tonearm will hang above the record upside down). In this way I can adjust the eccentricity of a record without walking between the graduated scale and the platter.
The average 12 inch record has an eccentricity of 0,3 mm (classical music records about 0,2 mm). The eccentricity of the record at Youtube is 0,6 mm, so the horizontal to and fro movement is clearly visible.
An externally hosted image should be here but it was not working when we last tested it.
I have centred one record by hand – the centre hole of this new record is far too wide – and the result is an eccentricity less than 0,02 mm (the red laser dot is only moving up and down). The distance between the fixed pivot and the wall was 3,2 m.
After all, I am not satisfied about the result (the laser tonearm). Because I have to walk between the graduated scale and the platter to adjust the eccentricity. Therefore, I will shorten the tonearm even further to 10 cm. So the fixed pivot has to be above the record (the tonearm will hang above the record upside down). In this way I can adjust the eccentricity of a record without walking between the graduated scale and the platter.
Do you have any recordings where this FM induced pitch instability is clearly audible? I have tried and failed to hear anything on any of my records.
@Billshurv,
I have ordered some materials for the 2 non-concentric rings to centre records. So at the moment I cannot compare 2 exactly the same LP’s (music), one without centring and one perfect centred. I need some comparison, because the human brain is constantly correcting our input by senses. For example, when someone gets spectacles with mirrors that turn the world upside down, our brain will correct the image after one or two days.
So when you look constantly through these spectacles for 2 days, you will at once see the world as before. Exactly the same with our ability to hear sounds. Therefore, we need a “fresh” comparison to hear the difference. And even then: our brain can switch immediately between different “filters”.
In the meantime I have changed the length of the laser arm to 10 cm (the pivot hangs above the record, see the image above). I have attached 2 mirrors to lengthen the distance between laser and graduated scale in an easy way (3 meter). Now it is possible to centre record on the “ kitchen table” .
I have ordered some materials for the 2 non-concentric rings to centre records. So at the moment I cannot compare 2 exactly the same LP’s (music), one without centring and one perfect centred. I need some comparison, because the human brain is constantly correcting our input by senses. For example, when someone gets spectacles with mirrors that turn the world upside down, our brain will correct the image after one or two days.
So when you look constantly through these spectacles for 2 days, you will at once see the world as before. Exactly the same with our ability to hear sounds. Therefore, we need a “fresh” comparison to hear the difference. And even then: our brain can switch immediately between different “filters”.
An externally hosted image should be here but it was not working when we last tested it.
In the meantime I have changed the length of the laser arm to 10 cm (the pivot hangs above the record, see the image above). I have attached 2 mirrors to lengthen the distance between laser and graduated scale in an easy way (3 meter). Now it is possible to centre record on the “ kitchen table” .
You do realise you see the world upside down from birth? The image on your retina is inverted. The mirrors would put it the right way up. I'm not interested in a before and after, but rather an audible example of before. There is a theoretical issue here, but no consensus on audibility. With all the research you have done surely you can find an example of clearly audible frequency variation?
Tom,
If you put a mirror on the tonearm and reflect the laser to the wall, you double angular resolution.
jn
If you put a mirror on the tonearm and reflect the laser to the wall, you double angular resolution.
jn
@billshurv,
First, there are tests. The fluctuations of the test frequency by eccentricity are about 25 Hz when the test frequency is 3150 Hz. I can produce the same frequency by a music instrument and measure the difference of 25 Hz. That’s just out of tune.
I have a test record that’s about 0,5 mm eccentric and when I listen to a test frequency of 300 Hz I can clearly hear the deviation every 0,9 second. Nevertheless, I don’t hear the deviation when it is not a test frequency but a normal LP with music. So my conclusion is that the deviation is masked by all the frequencies that are audible at the same time.
@jneutron,
You are right, a mirror can enlarge the angular resolution. Unfortunately, the shape of the red laser dot will alter horizontally too (smeared out). At the moment I use 2 mirrors to reflect the laser dot nearly 180 degrees. Just to keep the red dot small and the whole alignment compact.
First, there are tests. The fluctuations of the test frequency by eccentricity are about 25 Hz when the test frequency is 3150 Hz. I can produce the same frequency by a music instrument and measure the difference of 25 Hz. That’s just out of tune.
I have a test record that’s about 0,5 mm eccentric and when I listen to a test frequency of 300 Hz I can clearly hear the deviation every 0,9 second. Nevertheless, I don’t hear the deviation when it is not a test frequency but a normal LP with music. So my conclusion is that the deviation is masked by all the frequencies that are audible at the same time.
@jneutron,
You are right, a mirror can enlarge the angular resolution. Unfortunately, the shape of the red laser dot will alter horizontally too (smeared out). At the moment I use 2 mirrors to reflect the laser dot nearly 180 degrees. Just to keep the red dot small and the whole alignment compact.
I would suggest you try with pink floyd 'wish you were here' album. first track has about 2minutes of the same note. if there is a problem with the average 0.2-0.3mm offset you claim then it should not only be easily audible, but repeatable. any self respecting music fan will have that album somewhere.
At 3150Hz a semitone is 189Hz so your 25Hz is 0.7% and if its 25Hz total, not +/-25Hz then we are talking about beyond the limits of all bar those with absolute perfect pitch. The natural vibrato used by singers and players will be higher than this.
Possibly this is something that only people with very well tuned pitch sensitivity can hear, coupled with the visual cue of the arm moving.
Possibly this is something that only people with very well tuned pitch sensitivity can hear, coupled with the visual cue of the arm moving.
Glue a polished aluminum mirror to a copper flat, cure it at an elevated temperature. At room, it will go concave. Two test pieces will get you enough info to produce the focal length you need to make the spot sharpest.
Setup a tonearm reflector.
Setup mirrors so that the laser reflects off the platter edge, then to the tonearm reflector, then to the wall.
Mark the turntable edge every 10 degrees.
Put 36 reflectors on the edge of the turntable, one at each mark. Glue them such that each reflector makes the beam angle up or down based on the sine of the angle on the platter. At zero, no up/down. At 90, set the reflector so that the spot rises 10 mm (for example), zero at 180, -10 at 270.
The end result will be a lissajous pattern on the wall. Vertical will indicate angle of platter, horiz indicates groove offset scaled. A perfect record will provide a straight line up-down. An offset groove will produce a lissajous which indicates how much offset and what angle on the platter it is at.
Knowing the angle and the offset, a simple center mechanism can be designed to set the hole. Either a two screw system to offset the center in x and y, or a single screw setup which can be rotated to a specific angle.
jn
@billshurv,
It is about 25 Hz for the average record (~0,3 mm eccentricity) when the test frequency is 3150 Hz. And... it is – same eccentricity – 1,9 Hz at a frequency of 440Hz. The test frequency of 3150 Hz is “subject” because there are a lot of measurements (app en test record by “dr. Feickert”). At lower frequencies the deviation is simpler to hear.
Nevertheless, you don’t have to worry about eccentricity. I have never said you have too. I am only investigating the problem. You better can ask other people why they dream about extremely expensive turntables when the eccentricity of a vinyl record is the cause of more instability than a good turntable.
@jneutron,
Ingenious, but it is a lot of work. I hope you don’t mind that I am satisfied with the simple solution at the moment (and... a lot of platters have a drive belt arond). But maybe it is a nice project for others interested in the subject.
It is about 25 Hz for the average record (~0,3 mm eccentricity) when the test frequency is 3150 Hz. And... it is – same eccentricity – 1,9 Hz at a frequency of 440Hz. The test frequency of 3150 Hz is “subject” because there are a lot of measurements (app en test record by “dr. Feickert”). At lower frequencies the deviation is simpler to hear.
Nevertheless, you don’t have to worry about eccentricity. I have never said you have too. I am only investigating the problem. You better can ask other people why they dream about extremely expensive turntables when the eccentricity of a vinyl record is the cause of more instability than a good turntable.
@jneutron,
Ingenious, but it is a lot of work. I hope you don’t mind that I am satisfied with the simple solution at the moment (and... a lot of platters have a drive belt arond). But maybe it is a nice project for others interested in the subject.
Awww, that's no way to think...
Ok, put an optical encoder on the platter, use a camera and a computer to measure actively the location of the laser dot. It'll tell you what the offset angle and distance is..I know, someone can write an app!!
But I do mind...what's the fun in doing simply what can be done complexly with lots and lots of high falutin technology... it needs to be so incredibly complex, that nobody is able to completely understand the technology.
Like under the hood of my car..😱
jn
@jneutron,
Isn't it easier to take up a study theoretical physics at an university? That’s so incredibly complex, that nobody is able to completely understand reality! ;-))
Isn't it easier to take up a study theoretical physics at an university? That’s so incredibly complex, that nobody is able to completely understand reality! ;-))
Well in doing some more research to find out if anyone can hear this other than a fixed frequency I came across this Turntable speed analysis - pink fish media where in trying to measure motor frequency anomalies they can also measure eccentricity. Sadly no measure of audibility again. Certainly nothing worth drilling a huge hole in a record for.
I wonder why we have to deal with this defect. Because a defect it is and a huge one! A record pressing plant should deal with the problem, not the end users. I know the problem exists as long as the invention of the medium but that is not the issue here. A product should comply with certain quality standards and if not the manufacturer should take his responsibility and correct the problem. I have many records here, most in fact, that show not a single defect other than the occasional clicks and maybe a slight warp. Nothing to be worried about. But eccentricity of one or both record sides is not acceptable and quite avoidable if.....yes if, more care is taken by the pressing plant. Is that too much asking or what? If no one complains nothing will change. Drilling larger holes is just one method but it immedialtely makes the record a worthless item. I certainly would not want such a record treated in such a way. My method is not drilling out centers. I only make the center hole a little bit wider by using a very fine round file. One that fits the hole as good as possible. Only one or two twists of the file will do. Carefully remove all vinyl particles that came of prior to putting the record back into its sleeve. Job done.
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