Lathe/Turntable speed stability: Additive or Cancelling Errors?

RBFC

WBF Founding Member & Super Moderator
Apr 20, 2010
5,134
18
315
Albuquerque, NM
www.fightingconcepts.com
#1
The recent discussion of cutting lathes and turntable playback got me thinking (always dangerous).

It is possible that any speed instability in the cutting lathe might be shown or hidden by the turntable during playback if certain conditions are met.

1. Lathe: slight speed increase/Turntable: slight speed decrease AT THE SAME PLACE ON THE RECORD
may result in no perceived speed instability, as each error offsets the other

2. Lathe: slight speed increase/Turntable: slight speed increase AT THE SAME PLACE ON THE RECORD may result in increased speed error and be more easily perceived.

Therefore, it's conceivable to understand how a record might sound different on subsequent plays on the same turntable, depending on when you cued the stylus down and where in the "cycle" of the turntable speed instability you end up.

Thoughts?

Lee
 

mep

Member Sponsor & WBF Founding Member
Apr 21, 2010
9,483
6
0
#2
The recent discussion of cutting lathes and turntable playback got me thinking (always dangerous).

It is possible that any speed instability in the cutting lathe might be shown or hidden by the turntable during playback if certain conditions are met.

1. Lathe: slight speed increase/Turntable: slight speed decrease AT THE SAME PLACE ON THE RECORD
may result in no perceived speed instability, as each error offsets the other
I think the chances of this occurring are slim to none.

2. Lathe: slight speed increase/Turntable: slight speed increase AT THE SAME PLACE ON THE RECORD may result in increased speed error and be more easily perceived.
This condition would definitely result in increased speed error because you have just increased the error by another factor.

Therefore, it's conceivable to understand how a record might sound different on subsequent plays on the same turntable, depending on when you cued the stylus down and where in the "cycle" of the turntable speed instability you end up.

Thoughts?

Lee
I believe that records sound different on subsequent back-to-back plays because of the temporary groove deformation due to the heat from the stylus pressure. I don’t think it has anything to do with your speed stability or lack thereof.
 

RBFC

WBF Founding Member & Super Moderator
Apr 20, 2010
5,134
18
315
Albuquerque, NM
www.fightingconcepts.com
#3
I"m aware of groove deformation and heat effects being implicated in sound quality differences. I just had to wonder if we could be seeing another layer of error caused by mismatch in speed.

Lee
 

garylkoh

WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
5,462
40
545
Seattle, WA
www.genesisloudspeakers.com
#4
I believe that records sound different on subsequent back-to-back plays because of the temporary groove deformation due to the heat from the stylus pressure. I don’t think it has anything to do with your speed stability or lack thereof.
Mark,
I tried to test this by comparing two plays of the same record, but the speed instability swamps any other measurement I could make. Even adding a regenerating power conditioner (the old PSAudio) didn't help with the speed instability. Since the speed instability seems to be random, my guess is that it is the turntable, and not the lathe. I think that Bruce also tried it with two tracks recorded on Mike's Rockport Sirius and that's a direct drive - the speed instability is still there, but less than on my belt-drive.
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 23, 2010
3,730
101
520
Monument, CO
#5
<Long post typed then wiped by bad key stroke -- aaarrrggggghhhhh!!!>

Forgive if this has been stated and/or is well-known, but speed stability/variation is a bear to measure. I have measured an isolated system, just turntable and monitor system in an anechoic chamber, then repeated with the TT in a listening room. In the first case, the measurement results were repeatable; in the second, they were not, and did in fact appear random.

Speed fluctuations can be caused by so many things: line frequency variation, line noise (or supply), belt flexure (which may have periodic and random components), motor issues (friction, bearing wear, pole field variation, etc.), suspension/isolation issues (sound from the speakers can couple into the TT system, people walking across the floor, even air currents across the TT can introduce slight variations), platter mass density (introducing a bit of rumble), platter position (if not perfectly level can introduce a speed ripple), etc. etc. etc.

Bottom line for me is that speed stability, or variations, can come from so many things that it’s hard in the real world to correlate them to any one parameter. Measuring a TT in isolation provides a baseline, but its value to the end user is questionable except for marketing purposes.

All IMO! - Don
 

mep

Member Sponsor & WBF Founding Member
Apr 21, 2010
9,483
6
0
#7
Gary-Your TT has random speed variations all over the place? Do you see that with a strobe or is just under real playing conditions that motor can't stay at a constant speed when dragging a stylus through the grooves?

Mark
 

FrantzM

Member Sponsor & WBF Founding Member
Apr 20, 2010
6,464
6
255
#8
Hi

I wanted to ask the same question : How was the speed instability measured ?
 

Bruce B

WBF Founding Member, Pro Audio Production Member
Apr 26, 2010
6,812
211
560
Seattle, WA
www.pugetsoundstudios.com
#9
Hi

I wanted to ask the same question : How was the speed instability measured ?
The same track was played numerous times and digitally recorded. When you line the files up in a workstation, at certain points along the time-line the music track drifts a few to a lot of samples and back.. like a yo-yo effect.
 

tony ky ma

Industry Expert
Aug 22, 2010
627
2
18
Whitby Ontario Canada
#10
I don't think there will have a perfect LP repro system exist, so many little things can affect to the sound quality as Don listed, for hobby only what we can do is add or change things to the system which we have and see the result, like my friend he put a lot of ebony root to his system ( I posted his pictures in gallery) to find out the change, no matter change to good or bad just match to his favor will be alright , have fun is the main thing in this hobby
tony ma
 

garylkoh

WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
5,462
40
545
Seattle, WA
www.genesisloudspeakers.com
#11
The same track was played numerous times and digitally recorded. When you line the files up in a workstation, at certain points along the time-line the music track drifts a few to a lot of samples and back.. like a yo-yo effect.
Like Bruce says....

He lined up the files on a workstation, so probably far more accurate than what I did which was to use DiffMaker by Liberty Instruments. Listening to a constant 1kHz tone or 400Hz tone, the variation is barely noticeable, but after knowing what to listen for, I notice it more now.
 

mep

Member Sponsor & WBF Founding Member
Apr 21, 2010
9,483
6
0
#12
I guess the scary thing is that even MikeL's mighty Rockport didn't keep the speed dead-nuts on either though it was better. Maybe this is a big indictment of belt-drive technology. I have the VPI TNT with SDS. When I put a strobe disc on it, the speed looks *perfect* to me. I guess as soon as you drop the needle in the groove that things change. I have to say that I don't hear any speed variation on my set-up.
 

garylkoh

WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
5,462
40
545
Seattle, WA
www.genesisloudspeakers.com
#13
Mark, we were sampling at 96kHz and the drift was a "a few to a lot" of samples. Since I didn't know how to align samples on a DAW, I don't know what Bruce meant by "a few" or "a lot". At 96kHz, it will take 100 samples to be a 0.1% speed drift. I don't think that you can see that with a strobe disc.
 

mep

Member Sponsor & WBF Founding Member
Apr 21, 2010
9,483
6
0
#14
Mark, we were sampling at 96kHz and the drift was a "a few to a lot" of samples. Since I didn't know how to align samples on a DAW, I don't know what Bruce meant by "a few" or "a lot". At 96kHz, it will take 100 samples to be a 0.1% speed drift. I don't think that you can see that with a strobe disc.
Or hear it?
 

mep

Member Sponsor & WBF Founding Member
Apr 21, 2010
9,483
6
0
#16
I guess I can see why a good direct drive table will have better speed stability than a belt drive. I think Technics used to advertise that you could hook up 50 tonearms tracking at 15 grams each and play them all at the same time on the SP-10 and it wouldn't affect the speed. Bold claim. But maybe just maybe, the speed stability of the Technics SP-10 is what draws people to it and why they think it sounds better than most other tables.
 

fas42

Addicted To Best
Jan 8, 2011
3,973
0
0
NSW Australia
#17
I'm curious that no-one has appeared to mention what I always "knew" to be a problem with LP playback: whether the the record is actually perfectly centred on the TT during playback. There are at least two factors involved: was the centre hole perfectly punched; and how much clearance between the spindle and edge of hole, a larger gap meaning every time the record was taken off and replaced the speed wobble would be different. That 650K TT with its video monitoring should have that as a mechanism, a means of micro adjusting the lateral position of the disc until a groove sits at a very, very slightly decreasing radius from the centre of spin -- this should mean optimum speed constancy.

Frank

Frank
 
#19
I think that Chris Brady of Teres used and designed his Teres Certus turntables (including my Certus 450) with the Direct Drive Motor for maintaining the speed but teamed it up with the extreme 60 pound platter weight so that inertia would tend to keep the platter traveling at as close to perfect speed as was possible at the time of the design.

Rich
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 23, 2010
3,730
101
520
Monument, CO
#20
Thanks, Don. I was quite surprised when I discovered this speed fluctuation. I had thought that it might produce slight variations, but I didn't expect this much of a difference when comparing two tracks using Audio DiffMaker.
One obvious thing I forgot to mention, mainly because it is not random, is the variation due to the record itself. Mass density variations in the vinyl can again cause a bit, but the largest contributor in my experience is the hole in the middle. It is rarely perfectly centered (though is usually awfully darn close!) and if it is loose the record can shift a bit during play. The former is clearly correlated, but the latter is trickier... If the hole is large enough so the record can shift, then it can be affected by other things both random and not (platter/motor wobble, plater/mat friction, etc.)

Of course, I left off the impact the tonearm might have due to friction in its bearings, mass/momentum, counterweight, anti-skate, position on the record, and all that jazz. The cartridge could also vary a bit depending upon the track (position) and all the other factors.

It's a wicked complicated playback system.

BTW, the measurement system I used (actually, helped use) was optical, with a special thin metal platter of carefully control density and thickness, with dark "slots" to allow the optoelectronics to gauge speed. Our first trials involved a Hall effect sensor, but you need magnets and there was always a question of magnet placement and density.


Edit: I see Frank mentioned record hole centering -- should have read ahead a page!
 

About us

  • What’s Best Forum is THE forum for high-end audio, product reviews, advice and sharing experiences on the best of everything else. A place where audiophiles and audio companies discuss existing and new audio products, music servers, music streamers and computer audio, digital to audio converters, turntables, phono stages, cartridges, reel to reel, speakers, headphones, tube amplifiers and solid state amplification. Founded in 2010 What's Best Forum invites intelligent and courteous people of all interests and backgrounds to describe and discuss the best of everything. From beginners to life-long hobbyists to industry professionals we enjoy learning about new things and meeting new people and participating in spirited debates.

Quick Navigation

User Menu

Steve Williams
Site Founder | Site Owner | Administrator
Ron Resnick
Site Co-Owner | Administrator
Julian (The Fixer)
Website Build | Marketing Managersing