How about a little physics talk?
- Thread starter Bob_in_OKC
- Start date
ripblade
Super Member
Thanks for the explanation LD. Yes, it makes sense if we view the cartridge as a 2 channel seismometer with the sensors merely 3mm apart, give or take...both channels would pick up essentially the same data. However, what we perceive is not just pitch variation but also amplitude, and in this regard the channel with higher amplitude pitch variations will be the more noticeable one, I would think.
Just guessing, but it seems a reasonable explanation to my mind. What I should do is record a tone and, instead of summing to mono, duplicate left and right channels so that one file is L+L and the other R+R, then listen for which file has the more obvious pitch variation.
luckydog
Canis inquirit
Woodj, each time we place a record on a platter we set up a unique set of conditions. As to interaction between record imperfections, rotational imperfections, and arm stability etc etc. So each record play is wonderfully unique, to a measurable and sometimes audible extent IME !
Each record listening could be a moment to savour that will never happen exactly again
I believe the the tool itself to yield remarkably consistent results, as I think can be seen from consistency of L&R plots, and successive rotation plots recently posted.
Somehow, interpretation of succesive test results needs to embrace these things I think !
All just my 2p worth as ever !
Each record listening could be a moment to savour that will never happen exactly again
I believe the the tool itself to yield remarkably consistent results, as I think can be seen from consistency of L&R plots, and successive rotation plots recently posted.
Somehow, interpretation of succesive test results needs to embrace these things I think !
All just my 2p worth as ever !
luckydog
Canis inquirit
Hi ripblade, I doubt that would work as a test, because for sure there would also be channel amplitude and noise variations that you would also hear. I'd be amazed if pitch perception wasn't affected.
As I see it, the reason pitch stability affects L&R channels identically is that there is only one stylus ! As pitch stabilty on a mono track simply equates to relative speed of stylus and groove, it just can't be different between L&R channels when there's only one stylus. I think it's as simple as that !
luckydog
Canis inquirit
Just for amusement, here's a little holiday competition!
I've attached a new pitch stability plot which shows one revolution each from two TTs, in red and blue respectively.
They are 3rd party 3150Hz drops from different sources. One is said to be for a very well repected rim drive TT with excellent reputation. The other from an equally well respected direct drive TT, also with excellent reputation.
Question 1 Which is which?
Question 2 How can you tell?
Question 3 Which is better?
Enjoy !
I've attached a new pitch stability plot which shows one revolution each from two TTs, in red and blue respectively.
They are 3rd party 3150Hz drops from different sources. One is said to be for a very well repected rim drive TT with excellent reputation. The other from an equally well respected direct drive TT, also with excellent reputation.
Question 1 Which is which?
Question 2 How can you tell?
Question 3 Which is better?
Enjoy !
Attachments
gusten
Addicted Member
It seems to me the red is a bit better. It has a reasonable part of the round very close to 3150, also as a whole less higher frequency variations.
The blue would seem more difficult to get at 3150 with the same variations as the red.
My guess is the red is DD, and knowing myself, everything is most likely the opposite.:scratch2:
Also much of the variations on the blue could be down to a lesser arm, but of course not the lower pitch as a whole.
The blue would seem more difficult to get at 3150 with the same variations as the red.
My guess is the red is DD, and knowing myself, everything is most likely the opposite.:scratch2:
Also much of the variations on the blue could be down to a lesser arm, but of course not the lower pitch as a whole.
woodj
Super Member
I'm thinking the red is the rim drive and the blue is DD.
I am assuming the variation in the blue trace are corrections in DD speed.
I think the eccentricity connotes effects of the rim being pressured to one side (slightly).
I think the red is better because even though it is more eccentric, it shows less "spurious" "stuff.
I am assuming the variation in the blue trace are corrections in DD speed.
I think the eccentricity connotes effects of the rim being pressured to one side (slightly).
I think the red is better because even though it is more eccentric, it shows less "spurious" "stuff.
I'm with woodj, I think the Red is the rim drive, with the regular offset of pitch being due to possibly a slight eccentricity in the rim drive - it just doesn't make sense a DD having a steady pitch variation at that rate...
Other than this eccentricity the overall pitch stability appears better on the red... due to a very massive platter perhaps?
The blue (dd?) has more frequent minor variations could perhaps use more mass to smooth things out ?
Other than this eccentricity the overall pitch stability appears better on the red... due to a very massive platter perhaps?
The blue (dd?) has more frequent minor variations could perhaps use more mass to smooth things out ?
luckydog
Canis inquirit
Thought I might expand the contest a bit with one more sample!
Attached is a pitch stability plot in green, one revolution from a 3rd party sample said to be from another well known, respected and reputedly excellent TT.
Bonus Question 1
Is the TT
a) belt drive with suspended platter ?
b) direct drive ?
c) rim drive ?
Bonus Question 2 How can you tell ?
Bonus Question 3 Is it better than the other two TTs in previous question?
PS it is a 3kHz test tone !
Attached is a pitch stability plot in green, one revolution from a 3rd party sample said to be from another well known, respected and reputedly excellent TT.
Bonus Question 1
Is the TT
a) belt drive with suspended platter ?
b) direct drive ?
c) rim drive ?
Bonus Question 2 How can you tell ?
Bonus Question 3 Is it better than the other two TTs in previous question?
PS it is a 3kHz test tone !
Attachments
woodj
Super Member
Some guesswork here.
My first guess would be marginally "clocked" DD but, after further study, and looking at the pitch (in)stability, it could be a less than stellar belt drive or belt drive with clocked rather than 60 cycle motor. There are probably too many variations in pitch for it to be DD.
I think red is better.
My first guess would be marginally "clocked" DD but, after further study, and looking at the pitch (in)stability, it could be a less than stellar belt drive or belt drive with clocked rather than 60 cycle motor. There are probably too many variations in pitch for it to be DD.
I think red is better.
marcmorin
RIP 1953-2020
Thought I might expand the contest a bit with one more sample!
Attached is a pitch stability plot in green, one revolution from a 3rd party sample said to be from another well known, respected and reputedly excellent TT.
Bonus Question 1
Is the TT
a) belt drive with suspended platter ?
b) direct drive ?
c) rim drive ?
Bonus Question 2 How can you tell ?
Bonus Question 3 Is it better than the other two TTs in previous question?
PS it is a 3kHz test tone !
A) It's a suspended beltdrive
2) I see the spring filter frequency, and suspension reacting to arm/cart resonate frequency
3) no......it's running very slow
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woodj
Super Member
A little more babbling:
I seems the concentricity of the blue is better, but I think red would be the best of all in terms of less distortion.
Concerning the green, it is almost as if the TT would be suspended belt wherein unwanted pitch is being introduced by effects from the suspension of the (fixed) motor and the floating table assembly i.e. table bouncing, belt stretching or walking etc.
Perhaps, you are educating (or clouding our vision - the shadow knows) us, and this is a TOTL belt drive
I seems the concentricity of the blue is better, but I think red would be the best of all in terms of less distortion.
Concerning the green, it is almost as if the TT would be suspended belt wherein unwanted pitch is being introduced by effects from the suspension of the (fixed) motor and the floating table assembly i.e. table bouncing, belt stretching or walking etc.
Perhaps, you are educating (or clouding our vision - the shadow knows) us, and this is a TOTL belt drive
ripblade
Super Member
I wouldn't even hazard a guess.
Assuming all external influences which could potentially skew the results were somehow omitted from the plots, I might guess that the green one was the belt drive as well, but then I live less than 300m from a commuter rail line, and even less than that to the streetcar downtown. Construction and traffic is all around me, disturbing the ground under my house...and my turntable. Doesn't matter what the drive system is under these circumstances...isolation plays a much bigger role...as does the time of day the recordings are made!
Other than that, these are 3 different records as well?
Assuming all external influences which could potentially skew the results were somehow omitted from the plots, I might guess that the green one was the belt drive as well, but then I live less than 300m from a commuter rail line, and even less than that to the streetcar downtown. Construction and traffic is all around me, disturbing the ground under my house...and my turntable. Doesn't matter what the drive system is under these circumstances...isolation plays a much bigger role...as does the time of day the recordings are made!
Other than that, these are 3 different records as well?
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luckydog
Canis inquirit
Yes, personally I don't find it easy even to tell the drive type simply from looking at the plots and spectra, and overall the outcomes here are not bad in the scheme of things, IMO.
The samples are from 3rd party drops from rigs of different pretty knowledgable posters, where in good faith AFAIK there was no known fault or complaint about pitch stability. They naturally used different but good reputation arms/carts, and used different test discs.
I believe the rigs are each what many here might describe as 'achievably aspirational'. And each TT is well known and well respected and rightly sought after, but not 'super-fi' rare. I don't like to say what the TT models are though. Because I wasn't out to compare specific models, and this test is just a random slice through what I consider to be obtainable upscale performing TTs. If you guessed a few models in each class, I expect you'd include them !
The red trace is indeed the DD, so well done to those who guessed it! Once per rev stuff is probably off centre record, or play in the record hole that's most common IMO. If that could be sorted, to me this was the most pitch stable. If one just used a single number for w&f, it would probably come out worst though, just because of the eccentricity !
The blue then is the rim drive! The TT model has an excellent reputation for pitch stability, 'CD like' some say Well here it looks to me as though perhaps cart/arm stability contributes quite a bit, and overall the rig appears less stable than the DD (red) IMO. Perhaps a happy coincidence, once per rev stuff, (eccentricity?) appears lower than the red trace. Motors can have cog signatures, though I'm not sure that shows up here, and I didn't show the spectrum.
And green is a belt drive with suspended platter, so well done to those who worked it out! Yes, the spectrum in this case indeed has a big clue I think. More subtle is the way that oscillation seems to grow (time goes clockwise), which I think is different from cart/arm stabilty which seems to decay IMO. There is a bit of both here I think. The overall result is not bad IMO, but I agree it's the worst of the three in this case. Long term speed offset seems a common bane of friction drives generally, though as I say there was no complaint from the owner in this case, despite it being a decent model TT.
Overall, I'd grade them good- to good+ i think, at least by standards of what people seem to accept.
Lastly, thought I'd post one of my own plots, the result of changes and developments I made using this tool for my own use. Two successive revolutions, 3kHz tone. I can still just hear test tone variations, but to me enjoyment of music such as solo piano has improved massively, and I think the limiting factors now are virtually certainly in records themselves.
All just my own 2p worth of ramblings and opinions.
So, can you now tell what sort of TT drive it has ?
The samples are from 3rd party drops from rigs of different pretty knowledgable posters, where in good faith AFAIK there was no known fault or complaint about pitch stability. They naturally used different but good reputation arms/carts, and used different test discs.
I believe the rigs are each what many here might describe as 'achievably aspirational'. And each TT is well known and well respected and rightly sought after, but not 'super-fi' rare. I don't like to say what the TT models are though. Because I wasn't out to compare specific models, and this test is just a random slice through what I consider to be obtainable upscale performing TTs. If you guessed a few models in each class, I expect you'd include them !
The red trace is indeed the DD, so well done to those who guessed it! Once per rev stuff is probably off centre record, or play in the record hole that's most common IMO. If that could be sorted, to me this was the most pitch stable. If one just used a single number for w&f, it would probably come out worst though, just because of the eccentricity !
The blue then is the rim drive! The TT model has an excellent reputation for pitch stability, 'CD like' some say
Well here it looks to me as though perhaps cart/arm stability contributes quite a bit, and overall the rig appears less stable than the DD (red) IMO. Perhaps a happy coincidence, once per rev stuff, (eccentricity?) appears lower than the red trace. Motors can have cog signatures, though I'm not sure that shows up here, and I didn't show the spectrum.And green is a belt drive with suspended platter, so well done to those who worked it out! Yes, the spectrum in this case indeed has a big clue I think. More subtle is the way that oscillation seems to grow (time goes clockwise), which I think is different from cart/arm stabilty which seems to decay IMO. There is a bit of both here I think. The overall result is not bad IMO, but I agree it's the worst of the three in this case. Long term speed offset seems a common bane of friction drives generally, though as I say there was no complaint from the owner in this case, despite it being a decent model TT.
Overall, I'd grade them good- to good+ i think, at least by standards of what people seem to accept.
Lastly, thought I'd post one of my own plots, the result of changes and developments I made using this tool for my own use. Two successive revolutions, 3kHz tone. I can still just hear test tone variations, but to me enjoyment of music such as solo piano has improved massively, and I think the limiting factors now are virtually certainly in records themselves.
All just my own 2p worth of ramblings and opinions.
So, can you now tell what sort of TT drive it has ?
Attachments
gusten
Addicted Member
Really an excellent plot ld! About as good as it gets maybe, and these things don´t happen by themselves. And I certainly agree, the sonic benefits are there if everything is stable, and the polar plots appears to be an excellent way to explore the overall stability.
As for the drive, I don´t think a belt-drive, could be either a rim or a DD can´t say for sure.
As for the drive, I don´t think a belt-drive, could be either a rim or a DD can´t say for sure.
marcmorin
RIP 1953-2020
I'm going to go against the "current" and say this is a belt drive. Non-suspended, two part platter. pitch stability has been achieved via drive and driven face, main bearing, and a modification to arm mostly in the counterweight area. Or, I could be full of "used oats".
luckydog
Canis inquirit
Thanks gusten ! Maybe, I haven't yet seen better, and yes for me it is the product of effort, not least in producing tools to analyse both speed and arm stability! Much lies in the arm/cart IME.
The drive here is fundamentally DD. Torque/inertia ratio is unusually low though, and servo bandwidth is low. The platter has higher inertia than you'd see in most DD's, and isn't particularly exactly balanced. So the TT has a sort of hybrid character, I suppose, and mechanics is set accurately. As you say gusten, these things don't happen by themselves IME, though actually the end result can be very simple really!
IMO much of the action as to stability also lies in arm/cart too. This arm is fluid damped in all directions. There's nothing exotic done with mass at the counterweight end or elsewhere.
All just my 2p worth as ever !
