This is half the fun which is why families of readings from the same person with the same disk are my preference for lookoing for patterns. Pink noise appears to vary horribly, so any measurements with those need to be taken with a pinch of salt.
The HF resonance within reason is easy to understand (cart L, cable C, input amp C.
The peak and steep roll of yes, but the dip you often see from 2kHzish upwards isn't easily modelled. Something causes it but what?
Of course if you are using digital correction you can just dial in a low Q peak to compensate if your record is accurate.
I think you would have to look at the exact measurement set-up to decide where the mid-range dip came from. Tone arm resonance? Head shell resonance?
This is what I see and it seems to at least roughly match some other results. This is a log sweep at constant velocity, flat pre-amp, no equalization (500Hz to 50kHz (48 actually)), and has been fairly repeatable with several setups. The groove modulation prevents this from going <500Hz. I don't see this being explained by tone arm or headshell resonance.
Attachments
So, this disk was cut without RIAA EQ? Very interesting.
I was going to ask whether that makes the bass frequencies too strong to track, but I see that the test tone starts at 500 Hz, which is basically where the bass part of the RIAA EQ stops.
As for the high end, there's no tracking issue, just S/N. So, not having the RIAA boost during cutting probably makes it easier to measure the playback system response without too many variables to account for.
Is this CBS Labs disk available for sale somewhere?
CBS Labs STR 120, unfortunately good luck finding one now. They were a stock item in the Audio Amateur store until the 80's.
One side is left/right/lateral/vertical at three groove diameters at -8dB re 3.54cm/sec @1kHz. The text says that this sets the minimum groove curvature of 18 microns at the innermost track to 20kHz. There are also constant amplitude 10-500Hz tracks. The track is 48 seconds long at 24 sec per decade.
IME these LP's were produced under laboratory conditions and most or all were optically verified. My impression is they did whatever they needed to the signal path in the lathe to get the desired results, something we have not been able to do. BTW the slight discontinuity at around 31.5s is an artifact I can't recall if it was a dimple in in the surface of this track or something else. The equipment used to do the sweeps were at this time mechanical devices and I have found a couple of range switching artifacts that might not show up when using tracking filters and chain drive chart recorders.
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Hi Scott,
At what level is roughly the noise level while playing a blank groove when projected in your recording image ?
Hans
The spot noise was about 10dB over lifted stylus at high frequencies. The software decimates the actual samples and shows the peak which exaggerates the visual appearance of impulsive noise.
Just a Grado, BTW this is mostly a help out/intellectual exercise for me at this point. I have no interest in $$$ carts and TT's.
I wonder if you’d get a different result with only one channel connected and the other open circuit. Are the channels slightly coupling magnetically in the cart causing cancellation which is then followed further up in frequency with resonance?
No interest $$$ carts from my side either. My customers can afford that stuff. I’m with the Ortofon Red and @billshurves stylus trick. Listening to Ella on the LS50’s with a sub bass right now. Wonderful stuff.
We have been looking for suggestions especially a way to test for some inherent property of these systems that is being missed. It's not extreme just a soft slow depression of 1 or 2 dB or so. I am not the only one who has observed this. I'm also happy to be totally wrong for some reason (or even my preferred cart is poop).
How did you get the test signal into the cartridge? I'm assuming you performed a frequency sweep or impulse response (hopefully the former, for the sake of the cartridge).
If you prefer to link to another thread where you've already discussed this, I'll just catch up there...
50 ohm source (Bode-100) -10dBm via 5K Caddock puts a bit over 10uV on the cartridge.
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No. Just like with the MMs.
The tests on the MI (AKG P8ES) with/without the moving iron show no difference
Cartridge dynamic behaviour
Cartridge dynamic behaviour
George
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