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Cartridge dynamic behaviour
Cartridge dynamic behaviour
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Old 21st March 2019, 11:30 PM   #901
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by Hans Polak View Post
Amplitude in that region will change its amplitude with speed, so 1.35x faster means 2.6dB more level, true ?
Yes, so you need to move the red line up 2.6dB on the 45 RPM plot so at 20k the difference is closer to -6dB vs -5.6dB not -6dB vs -3dB.
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Old 22nd March 2019, 12:15 AM   #902
scott wurcer is offline scott wurcer  United States
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Another way to explain, RIAA is flat at 1kHz so the red and green lines should always intersect at 1kHz reflecting only the RPM change.
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Old 22nd March 2019, 07:06 AM   #903
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by Hans Polak View Post
I have no idea where the constant amplitude stops and how the transition from constant amplitude to constant velocity happens.
It doesn't happen at all - it's an artificial construct aimed at helping understand what constrains limits of playback level at various frequencies.

Fortunately, no-one explained this to magnetic playback cartridges, which simply transcribe instantaneous stylus velocity into instantaneous cartridge emf or voltage output level. Nothing to do with frequency, at least in principle.

So if one considers playback of a sine wave f sweep with constant programme level and no RIAA emphasis, it would have constant stylus velocity across the band. If one changes rpm, only cart output level would change.

If one considers the same sweep made with RIAA 'on', f sweep velocity as recorded on the record is f dependent. So changes to rpm imply a mapping of 'old' RIAA level onto 'new' RIAA level, for playback to be flat, as well as scaling overall level.

LD

Last edited by luckythedog; 22nd March 2019 at 07:08 AM.
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Old 22nd March 2019, 10:03 AM   #904
Hans Polak is offline Hans Polak  Netherlands
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Originally Posted by luckythedog View Post
It doesn't happen at all - it's an artificial construct aimed at helping understand what constrains limits of playback level at various frequencies.

Fortunately, no-one explained this to magnetic playback cartridges, which simply transcribe instantaneous stylus velocity into instantaneous cartridge emf or voltage output level. Nothing to do with frequency, at least in principle.

So if one considers playback of a sine wave f sweep with constant programme level and no RIAA emphasis, it would have constant stylus velocity across the band. If one changes rpm, only cart output level would change.

If one considers the same sweep made with RIAA 'on', f sweep velocity as recorded on the record is f dependent. So changes to rpm imply a mapping of 'old' RIAA level onto 'new' RIAA level, for playback to be flat, as well as scaling overall level.

LD
Thank you for this information, this is exactly what I did.


I adjusted Level in the same ratio as the change in rpm, resp a and b in the image below.
And Mapping the old Riaa into the new Riaa was done accordingly with the same a and b.
a= (45)/(33 1/3) and b = (60.75)/(33 1/3)


So I think I did everything the way it should have been done.


Hans
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Old 23rd March 2019, 01:22 PM   #905
scott wurcer is offline scott wurcer  United States
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I'm kind of burnt out on trying to figure out all the error sources in using these various test LP's. If you know that your cartridge is a perfect velocity transducer at these levels it's one thing, mine is not so I needed the extra correction.
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Old 23rd March 2019, 06:51 PM   #906
Hans Polak is offline Hans Polak  Netherlands
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Originally Posted by scott wurcer View Post
I'm kind of burnt out on trying to figure out all the error sources in using these various test LP's. If you know that your cartridge is a perfect velocity transducer at these levels it's one thing, mine is not so I needed the extra correction.
You are applying Riaa in the digital domain, aren’t you
In that case it wouldn’t seem to be any problem for you to digitally remap the Riaa time constants when changing speed. After that, all that remains according to LD is a fixed level shift over the complete spectrum.
Or are you referring to something else with “extra correction”
In that case, what could be the reason for and the nature of this extra correction ?

Hans
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Old 23rd March 2019, 07:27 PM   #907
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by scott wurcer View Post
If you know that your cartridge is a perfect velocity transducer at these levels it's one thing...…….
But in reality cartridges are not perfect, despite whatever claims arise. This is obvious because in practice cartridges sound profoundly different, no matter what similarities they might possess under limited test conditions.

It just means one is measurng the wrong aspect of performance. I still expect to find a level sensitive answer, when eventually the secret is found.


LD
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Old 23rd March 2019, 08:26 PM   #908
scott wurcer is offline scott wurcer  United States
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Originally Posted by Hans Polak View Post
In that case, what could be the reason for and the nature of this extra correction ?

Hans
The cartridge is not a true velocity transducer. Your correction converges at high frequency to 0dB, this relies on the constant velocity behavior matching RIAA exactly, one up with f and one down with f at exactly the same rate.
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Old 23rd March 2019, 08:31 PM   #909
scott wurcer is offline scott wurcer  United States
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Originally Posted by luckythedog View Post
I still expect to find a level sensitive answer, when eventually the secret is found.
This is why I think 500Hz to 50kHz constant velocity sweeps without RIAA at several different levels would be useful on a test LP. The STR series had one LP with only the 505Hz time constant a reasonable compromise that allows sweeps that span the whole range. Taking the RIAA conformance of the lathe and your pre-amp out of the equation is a good thing.
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Old 23rd March 2019, 09:50 PM   #910
Hans Polak is offline Hans Polak  Netherlands
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Originally Posted by scott wurcer View Post
The cartridge is not a true velocity transducer. Your correction converges at high frequency to 0dB, this relies on the constant velocity behavior matching RIAA exactly, one up with f and one down with f at exactly the same rate.
O.k. , I’m with you because that was exactly the reason why I questioned in #582 whether it could be a square law instead of a linear relation between speed and level, because I was missing 1.3 dB when speeding up and also when going down in both cases by a factor 1.35
But the answer in #584 was a definite No.

So it seems we are back at this point after all.
Question is, what can we do to come closer to finding answers with the materials we have, because flat recorded LP’s with different levels are not available.
I can have a look again at my recordings and measure the exact level change versus the calculated level change.
Would that bring anything ?

Hans
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