Pinch Effect Distortion Calculator

[Guest]

A few threads came together since I last posted about pinch effect.

In one thread it was determined that, other than the effect of RIAA pre-emphasis, pinch effect simply depends on instantaneous groove angle. Which in turn simply depends on level, rotation speed and radius from the spindle. Peak vertical stylus displacement upwards (due to pinch effect)occurs at point B in the sketch below :

In another thread, it was determined that for real recordings, groove curvature radius at point A is greater than curvature radius of stylus for common elipticals and fine line stylii, and also for common sphericals (except for peak accelerations on inner grooves). So generally there is no pinch effect at point A due to curvature, the stylus is fully seated.

And in another thread, an equation defining the vertical displacement of the stylus due to pinch effect was uncovered :

references are at http://www.badenhausen.com/VSR_History.htm

Putting it all together, I added a simple calculator to Groovy.xls, that now reports vertical displacement and 2nd harmonic distortion due to pinch effect at B, as a function of stylus radius, level, frequency, spindle radius.

I think it's pretty useful in illustrating at what frequencies, levels, and inner groove radii, finer radius stylii make a difference. And how much overall harmonic distortion there unavoidably is.

It does highlight the benefits of fine radius stylii on distortion.

Usual caveats apply, as it's a test version, and I appreciate any return comments, and/or validation versus other sources.

The pinch effect distortion calculator is here :

[analogaudio]

That's neat, worst case seems to be towards end of side, at high frequency, conical (spherical) stylus, at high audio level, doesn't this make pinch effect a prime candidate for inner groove distortion? Any idea how much 3rd harmonic is created?

Ted

[Guest]

Thanks analogaudio. I was surprised at how rapidly pinch effect distortion rises toward inner grooves and with frequency too ! It would seem to correlate very well with inner groove distortion. If it looks like a duck and quacks...........!

Here's some tables that illustrate. Firstly for an eliptical (7um) radius stylus :

-10dB is pretty 'hot' at 10kHz + , of course, perhaps only just trackable on inner grooves. Level is post RIAA, ie as measured at preamp output after RIAA stage.

But one can see from this how distortion really cranks up toward inner grooves at high frequencies for loud levels.

Here's a table for same conditions, but with 3um (fine line) stylus :

Distortion's a lot better than eliptical at high frequency inner grooves. One can see the benefit of fine radius stylus here.

Here's a table for an 18um spherical :

Remember -10dB is pretty hot at 10kHz. The contrast with smaller radius stylii is extraordinary really. Also 2nd harmonic distortion for 10kHz is inaudible (being @ 20kHz), but IMD products might well not be.

These tables seem a great illustration of the benefits of fine radius stylii on inner groove high frequency distortion performance !

[Guest]

And then we have the stylus-groove wall "bounce" resonance, which, according to Norio Shibata, exists, and is significantly reduced by using an elongated contact footprint.

Thanks for the excel, ld. Priceless.

[Guest]

And then we have the stylus-groove wall "bounce" resonance, which, according to Norio Shibata, exists, and is significantly reduced by using an elongated contact footprint.

Thanks for the excel, ld. Priceless.

You're welcome, .

Yes, it's a seperate matter, and whatever the cause, that distortion effect is smaller but additive. That effect peaks at point A on the OP sketch, maximum deflection, (rather than B for pinch effect). And i think causes 3rd harmonic distortion, but that's another topic. In any event, pinch effect seems the big one !

[Guest]

I was able to validate pinch effect distortion results predicted by the Groovy calculator versus figures published on Yosh's recspecs page here http://www7a.biglobe.ne.jp/~yosh/recspecs.htm , for stylus radii of 5um and 18um, including variation with spindle radius, and the match is very good/excellent. So this is good news !

[Guest]

ld, my sincerest and deepest thanks. You are helping me to save money!

[Guest]

Interesting to see how in some cases the 2nd harmonic can go up to the ceiling!! Makes me remember what user 1200y3 said once, something like:

"Conicals give a bigger, fuller sound"

I replied saying that this was due to the added distortions... Seems we both were right!!

Currently i'm trying an old Pickering V15-AT2, an old-school MM with a nicely polished conical of med-low compliance (tracks at 2-5g); i'm using it at 3.5gm where it seems to have no tracking problems; and yes, it does have an 'enhanced' sound, particularly when comparing it to my current reference, the EPC-450CII (semiconductor cartridge, shibata tip, titanium cantilever, circa 0.3mg effective tip mass).

I do notice the sound is "louder" and i'm not talking about more voltage, but a sensation of loudness. It is well known that the harmonic distortion present on tube guitar amps fools the human ear into believing they are louder than they are!!

[Guest]

Can you guess which cartridge this advertising describes ?

Increased Presence and Clarity
Deeper, More Resonant Bass
....... Natural Brightness
Greater Perceived Loudness
Tighter Bass Articulation
Improved Detail and Intelligibility
Extended Low Frequencies

.........enhances detail, clarity and imaging.........increase intelligibility.......it pulls a vocal or an instrument up out of a mix........... adds low-end punch with deeper, more powerful bass.

Sounds neat, familiar even, and describes some of the features often sought after as desirable and popular amongst cartridges.

Unfortunately, it is actually advertising literature for an Aphex 204 studio exciter/enhancer ! Which is a neat little add on, that works by adding harmonic distortion, and a non-linear amplitude response (by accounts), and achieves its results through psycho-acoustic means. Aphex exciters were widely used in studios the 70s onwards, particularly on vocals. Overused some would say !

A fairly recent thread where a member puts the whole mix through an Aphex 104 here viewtopic.php?t=29070

So yes, adding the 'right type' of distortion can be pereived as improvement such as increasing detail/clarity/realism and all the trimmings. By some/most people anyways.

Strange old world sometimes, isn't it ? Such things fit the description of the 'house sound' of some carts and stylii pretty well IMO.

[Guest]

Actually, although pinch effect distortion is likely to be audible, especially on inner grooves, i doubt it can contribute such a spectrum of psycho-acoustic effects. After all, we all know what IGD sounds like, and even without mistracking, it's not too pretty really ! So I think comparison to an exciter is not too realistic, on second thought. But I like the idea it might contribute to 'fullness', warmth, or perceived loudness.

On a seperate point, I just realised how huge stylus acceleration associated with pinch effect vertical motion can be ! For inner grooves, high frequency loud levels it can approach similar accelerations as the original signal ! This is because the frequency is x2, and the amplitude is significant.

That would be OK, except a) Such accelerations are additional to existing normal vertical stylus acceleration b) Downward motion of the stylus is not driven by groove walls, it happens under influence of force applied via the cantilever - as the article posted by rorenoren on another thread pointed out.

So I wonder if downward stylus acceleration due to pinch effect is what really limits overall trackability on inner grooves at high frequencies and loud levels ? It fits pretty well. It explains why the mistracking point is generally at the quadrature (90 deg) point in a sinusoid cycle (at the point of highest pinch effect acceleration), that has always puzzled me.

That's interesting...... !