Why is reading crosstalk so inconsistent across the different tools?

[J.R. Boisclair]

I know I must seem like I'm completely hung up on crosstalk, but I just had more experiences from which I can only conclude that there is no reliable way to ever objectively set ideal crosstalk - it's all relative to the particular test record being used.

I decided to experiment. I found four copies of the old Command Test Record (CS100) is excellent or NM condition and bought them. This record has tracks for L and R crosstalk that contain a 1KHz signal in one channel and nothing on the other (like some other records), but it had been lauded by some in the analog world as being among the most accurately cut test records out there. I also bought two other copies of the AP Ultimate Analog test record. Including my other copy of the AP test record, I ran crosstalk measurements using the same softwares (A+ and the Visual Analyser oscilliscope) using all 7 records. The results were less than encouraging. The variation across results was up to +/- .9dB, consistently. That means depending on which two records one might use, if one shows the R to L difference of +.9 dB, the other would shows the L to R difference of + .9dB - a difference in crosstalk measurement of 1.8dB! More amazingly, the difference across just the AP Ultimate Analog test records was -.7/+.8 dB, a 1.5dB variation that, if choosing one measure as right and the other as “wrong”, would have the cartridge tilted in the completely opposite direction!

Frankly this suggests to me that the whole mania of trying to get anything right using any test record is nothing but random.

Not totally random at all. Results are simply explained by variation across a normal distribution curve. This means that if you took the average results over a large number of test records, you would be pretty damn close to perfect. However, you aren’t collecting enough information if you’re only looking at decibels. You have to watch the phase. If you did this, I think you would see a little better consistency across records.

The problem starts with the symmetry (or lack thereof) of the cutting stylus. As I’ve discussed in my videos, this is a big problem and very common. I have spoken with many mastering engineers and none of them inspect for this.

Not a single test record to date offers any assurance that their four cutting angles, cut path and stylus symmetry were defined and margin of error noted before cutting the lacquer. THEREFORE, not a single test record can be trusted as a reference for any given playback alignment test.

We are doing something about this.

 

[J.R. Boisclair]

It’s not particularly about cutting process. It’s about flatness of record.

A record might seem perfectly flat but it isn’t. There are minor warps over the record from outer groove to inner groove. The problem is you cannot flatten the record with clamping method you use. Actually only successful method I have encountered that can flatten those minor warps is vacuum hold down.

There is a distinct difference between AM and AP test records in terms of azimuth but I get same azimuth point when there is vacuum hold down. When there is no vacuum hold down perfect azimuth point differs slightly. This happened with every vacuum hold down turntable and none with others.

So, the problem is vinyl material and flattening record with a machine helps but vacuum hold down solves it.

I haven’t done a controlled variable test of this hypothesis. I think it is worth inspecting

 

[tony22]

Yes @mtemur, granted, I have only a periphery ring and a record weight, but have you tried to measure crosstalk across multiple copies of the same record?

 

[tony22]

You have to watch the phase

A+ does display phase for each direction of crosstalk. Within this range of variation seen for the separation measures, the phase didn’t vary by more than a few degrees. Here is just one example (of several).

 

[mtemur]

Yes @mtemur, granted, I have only a periphery ring and a record weight, but have you tried to measure crosstalk across multiple copies of the same record?

No, I haven't. If you have an ORB record flattener I recommend you to flatten those 3 AP records even if they look flat. After that check if azimuth readings are still differ 1.5dB.

 

[tony22]

If you have an ORB record flattener

I’ll have to borrow one.