Because low stylus-groove friction can have a profound effect on playback performance in a very broad sense: reduced harmonic distortion, reduced surface noise, improved cart-arm lf stability (pitch stability).
Harmonic distortion improvement is via improved accuracy of tracing: locus of the stylus more accurately follows locus of the groove base, stylus is less likely to ride up the groove wall when presented with steep groove angles. This is particularly true for offset angle arms, where the line of applied friction force produces a significant torque for the stylus to ride the inner groove wall.
Surface noise improvement is presumed to be via reduction in micro-mistracking: momentary loss of contact with one or both groove walls in response to momentary stick-slip type friction variation. Crackle-tick type surface noise.
Pitch stability improvement is via reduced instantaneous variation in skate force, giving rise to variation in torque to move the headshell.
Geometrically induced harmonic distortion, ie because there is a classic tracking offset angle, is small in the scheme of things compared to mistracing induced distortion. Mistracing meaning that the stylus base does not exactly follow the groove base locus.
One can readily calculate that 315Hz/3150Hz @-10dB ref 5cm/s is too quiet to show significant FM effects. That's not to say there won't be measurable IMD due to harmonic distortion arising from mistracing from all other sources, some of which can vary significantly with 3D stylus alignment.
3150Hz/1850Hz @-10dB stereo is reasonably hot and will rotate its vector, as previously discussed. I'd expect stylus alignment HD to affect HD/IMD on a track like that, via the mechanisms suggested above.
It's not that I doubt the usefulness and effectiveness of such tests, quite the opposite. Just that I doubt the common-wisdom explanation of the mechanisms involved................
VTA is one aspect, and lateral tracking offset angle is another. Might be worth trying deliberate lateral tracking offset angle error too, especially for finer radius styli - the sweet spot of IMD isn't necessarily the geometric 'ideal'........
LD
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I think that's probably the best indirect method, and needs to be lateral at +12dB ref 5cm/s, 4:1, plus a similar vertical track except for level which needs to be at the largest level likely to be trackable (which needs some thought to come up with)............
As to direct methods, a silent track that's long enough to allow for spin-down time tests, a few minutes long, and near the outside of the record. Followed by a heavily modulated track of similar duration, perhaps +12dB@1kHz ref 5cm/s.
Any other ideas for how? Click-free silent lock groove ? Several of them?
LD
Here the results of the 315Hz/3150Hz @-10dB 4:1.
Left is with 3 LP's, in my case changing the VTA by 1.5 degrees, right is with just the test disc and the VTA optimally adjusted.
FFT is calculated with a Hann Window.
Apart from the slight raise of the 3rd harmonic of the 315Hz tone, and the raise of the surface noise around the 3150Hz, there is little drama.
Hans
Left is with 3 LP's, in my case changing the VTA by 1.5 degrees, right is with just the test disc and the VTA optimally adjusted.
FFT is calculated with a Hann Window.
Apart from the slight raise of the 3rd harmonic of the 315Hz tone, and the raise of the surface noise around the 3150Hz, there is little drama.
Hans
Attachments
FYI Some of the tracks at the inner grooves threw the stylus out completely, I mean all the way out.
OK, thanks.
What is lateral vs vertical, in terms of the L&R signals? Is lateral mono?
So far results were not very promising with the radial tip, but also the Adjust+ LP, played with an eliptical stylus didn't reveal anything that could be used in adjusting the VTA or Stylus Friction for that matter ! (Posting 425 & 428)
I'm therefore anxious looking forward what your visit to Kevin will bring.
Hans
Under the circumstances that the test track is oddly quiet (see my post above), despite all there's definitely notable difference in both the noise floor and 400Hz IMD sidebands nearby 4kHz. And given the gross scale, I think it's fair to say the results are distinct despite a relatively small change in tracking angle (VTA in this case).
The frequency domain is not as good a way to look at this as the time domain, and chances are the sidebands indicate there might well be something FM worth looking for methinks. Both the noise floor and the sideband differences are probably a result of altered friction though, which is fair game and exactly what we might be looking for I think......
The test tracks aren't optimal at all for showing desired effect though........ hence the suggestion for test tracks as above.
LD
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