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Old 2nd January 2018, 09:08 PM   #1091
billshurv is offline billshurv  United Kingdom
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Quote:
Originally Posted by Hans Polak View Post
Our hearing system is especially sensitive to FM modulation for frequencies between 2.5 and 10Hz, exactly where the Cart resonance takes place.
As long as the LF IM products are below 0.1%, it will usually be inaudible.
That should be seen as an auditory threshold level.
Which is why I am planning to experiment with higher resonant frequencies. On another forum, where scientific types are expunged the answer is always to add more mass to the headshell. I'm just not convinced that 7Hz resonance is EVER good. But I would like to repeat the B&K measurements with adjustable damping.
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Old 2nd January 2018, 10:14 PM   #1092
scott wurcer is offline scott wurcer  United States
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Originally Posted by luckythedog View Post
.if someone has some time one rainy day might be interesting to use Scott's SW which can report AM in principle?

LD
I've done it, the magnitude of the Hilbert transform is the amplitude and the derivative of the unwrapped phase is the instantaneous frequency. I'll try and post a plot from one of the previous test runs.

I'm going to be doing some work while on holiday the next month or so redoing the filtering to accommodate the IEC wow and flutter and including a window for the spectrum and other information.
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Old 2nd January 2018, 11:24 PM   #1093
Pano is offline Pano  United States
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Thanks for the list, KevinH. I've wondered about putting out of phase or uncorrelated pink noise on the LP. I find those to be useful digital test signals but don't know how well they would cut in the low frequencies. TBD. Do you know what the absolute phase signal is? Maybe a sawtooth?

These days 1/3 octave bands of pink may not be as useful as they once were, now that we had computer analysis at hand.
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Old 3rd January 2018, 01:50 AM   #1094
diyrayk is offline diyrayk  United States
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Quote:
Originally Posted by Hans Polak View Post
That's not what I had in mind.
I wanted to see what the Arm/Cart is additionally contributing to IM distortion, which cannot be simply predicted by looking at the spectrum of a silent track.
I agree. I recommend a 3150Hz carrier with a superimposed LF sweep or discreet LF spot frequencies. 'Tickling' the arm/cartridge at the LF resonance this way really stirs up FM mud quickly, and some arm/cart combinations deteriorate more rapidly than others. Such a test is more useful than a silent groove to separate the wheat from the chaff.

Ray K
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Old 3rd January 2018, 10:01 AM   #1095
luckythedog is offline luckythedog  United Kingdom
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Originally Posted by diyrayk View Post
I agree. I recommend a 3150Hz carrier with a superimposed LF sweep or discreet LF spot frequencies. 'Tickling' the arm/cartridge at the LF resonance this way really stirs up FM mud quickly, and some arm/cart combinations deteriorate more rapidly than others. Such a test is more useful than a silent groove to separate the wheat from the chaff.

Ray K
Yes, I agree. This was demonstrated on a different thread a few months back as highly effective.

In post #654 such a test was suggested and included in the candidate list as a set of highly modulated bursts with a swept lf repetition frequency. But a continuous tone sweep could be just as effective, methinks. Originally it was lateral and vertical stimulus as separate tests, IIRC.

Such a test could go anywhere on the record. Sweep or spot frequencies need to progress slowly enough so that polar plot SW can determine well resolved results. It might take up, relatively, quite a bit of time on the record. But there should be plenty of inner groove space, methinks.

Sweep range 5Hz to 24Hz perhaps?

LD

Last edited by luckythedog; 3rd January 2018 at 10:08 AM.
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Old 3rd January 2018, 12:49 PM   #1096
Pano is offline Pano  United States
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Originally Posted by diyrayk View Post
I agree. I recommend a 3150Hz carrier with a superimposed LF sweep or discreet LF spot frequencies.
What ratio? Or 3150 in on channel, the sweep in the other?
The Telarc disk uses a 4-125Hz sweep, is that too broad?
Let me know, along with the duration, and I'll make us one.
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Old 3rd January 2018, 09:51 PM   #1097
diyrayk is offline diyrayk  United States
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Originally Posted by Pano View Post
What ratio? Or 3150 in on channel, the sweep in the other?
The Telarc disk uses a 4-125Hz sweep, is that too broad?
Let me know, along with the duration, and I'll make us one.
My gold standard for evaluating FM susceptability is the Ortofon Test Record #0001 and #0002, both lonnng out of print. Ortofon cut 2 tracks, one for vertical and one for horizontal. They superimposed a combination of 2349Hz and 2960Hz on a subsonic test sweep from 4 to 25Hz. The resonance test was for subjective evaluation and did not require the user to possess or use any instrumentation. I attached some of the liner notes that describe these test bands. Although the intent of the tone complex was to detrmine the mass/compliance resonance frequency (Fres), the mechanism by which the tone complex made the Fres point audible is the FM warble that the user heard when the vibrating arm caused stylus scrubbing. I think the DIY group's standardizing on 3150Hz would also accomplish the desired audible objective, plus the DIY tone complex would allow objective analysis of FM via software.

Please be aware that, for whatever baffling reason, the currently re-issued version of the Ortofon test record does NOT have these resonance test bands! (And neither does the out-of-print Ortofon Test Record #0003)

Ray K

http://www.diyaudio.com/forums/attac...1&d=1515019840
http://www.diyaudio.com/forums/attac...1&d=1515019840
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File Type: jpg Ortofon Res Test b.jpg (421.9 KB, 107 views)
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Old 3rd January 2018, 10:12 PM   #1098
Hans Polak is offline Hans Polak  Netherlands
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Ray,

I still don't get what the advantage would be to have a combination of 3150 Hz with a superimposed sweep from 4-25 Hz if the only purpose is to find out what Fres of the Cart/Arm is.
Just having a sweep from 4-25 Hz will do the same IMO.

And as we have seen in various plots, a single 3150 Hz tone will also reveal Fres in the IM spectrum.
My proposal to have a strong and a weak 3150 Hz signal, separates the TT noise without Fres from TT + Fres.
I do not see this info popping up with the 4-25 Hz chirp.

And on top of that, to know Fres as just a frequency seems less important as it is to see what it does to the IM distortion.

Hans
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Old 3rd January 2018, 10:18 PM   #1099
Pano is offline Pano  United States
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Thanks Ray. If you can Hans can work this out, let's add it to the track list. One, the other or both.
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Old 3rd January 2018, 10:38 PM   #1100
luckythedog is offline luckythedog  United Kingdom
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Quote:
Originally Posted by Hans Polak View Post
I still don't get what the advantage would be to have a combination of 3150 Hz with a superimposed sweep from 4-25 Hz if the only purpose is to find out what Fres of the Cart/Arm is.
Just having a sweep from 4-25 Hz will do the same IMO.
One advantage is that, by looking at FM effect of headshell motion on a 3150Hz carrier, one does not rely on absence of high pass filter roll-off in f amplitude response of preamp and/or cart gen looking a baseband lf. Which factors vary from rig to rig. This is helpful when evaluating Q of the resonance - the parameter that really matters.

Quote:
Originally Posted by Hans Polak View Post
And as we have seen in various plots, a single 3150 Hz tone will also reveal Fres in the IM spectrum. My proposal to have a strong and a weak 3150 Hz signal, separates the TT noise without Fres from TT + Fres.
Any difference between strong & weak carrier tone results is difficult to explain IMO. But could be due to increase in random friction/drag in the presence of modulated grooves I suppose. So if there's space, I vote to keep the split levels in anyway.

LD

Last edited by luckythedog; 3rd January 2018 at 10:42 PM.
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