How was the pink noise recorded, flat LP , flat preamp or resp. anti Riaa + Riaa preamp.
In both cases, how was the FR flattened, did your testgear have octave filters, if not I would have expected a 10db/oct slope.
What surprises me most is that there are two transitions, one at 350hz and one at 9.3kHz.
So could it be that these octave filters have transitions at these spots and that they are working at the edge of their sensitivity ?
In that case it would be a testgear thing and not a Cart problem.
Hans
That's 3.5k the scale is faint. There is no test gear just an averaged FFT of a recording of an ordinary RIAA equalized LP. Nothing is anomalous in the spectrum when you take out the FR of the cart BTW. The right channel is a blank groove so the cart has to be making everything you see there.
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I agree that the smaller the R in series with the Cart, the better the SNR if that is what you mean.
Playing with the resistors inside the filter can create almost any gain above a certain level for almost any thinkable MM Cart.
And thinking of SNR, a bit more gain as 20dB@1Khz for the first stage could help to diminish the noise contribution of the second stage to the overall noise.
Hans
yeah, it's 3.5kHz, I see it now.
Pink noise is at -21dB at 3kHz, so with 10dB/decade it should be at -24dB at 6kHz, -27dB at 12khz and at -30dB at 18kHz.
As from 7.5kHz a resonance is starting with a peak of 9dB @ Fr=13kHz and at 18kHz, noise is back where it was expected to be,
What exactly is resonating at this relatively low frequency, I have no idea, but it influences the noise in the blue channel just as much as it does in the pink channel, meaning that instead of moving just under an angle of 45 degrees, the cantilever starts to making funny movements at the point where the resonance is having a phase shift of ca. 45 degrees.
I need to take some other pink noise LP's and compare, as Bill said there is something about them that always seems a little off.
Curious for sure. If it's not a measurement artefact, then a series of eigen or bessel vibration modes? Q is very high though and it doesn't show in the left channel...….
LD
I ripped several test LP's last year to digital but never looked at some of the data. Strange behavior like this always intrigues me.
Finally found the measurements of L vs R I had been looking for courtesy of my friend Ron. These were taken with a Mastech MY6243 which measures L at 900Hz (where we want for this measurement). I'm not usually a fan of cheap stuff like with +/-5% FSD accuracy on the 2H range but tempted given the time it will take me to hook up a 'proper' rig it could be good enough for rock and roll and comparative measurements. Thoughts?
I'll chew the numbers and report back.
I'll chew the numbers and report back.
Just a quick check to see what a different system does, I played a pink noise track on my set, only one take.
I have no MM so this is recorded, with an MC Cart.
4 seconds at fs 44.1kHz, processed with Rightmark, 16.384 samples with 75% overlap, resulting in 8 averaged spectra, recorded from Hi-Fi news test LP.
If you want me to do some other test with different parameters, let me know. I also have an Adjust Plus test LP with pink noise that I could try.
There are also some "jumps" in the low channel at 3kHz and 8.8kHz, but I'm not sure whether these may be caused by dirt or small scratches in the LP, but nothing comes close to what you showed.
Hans
Attachments
Playing the same LP at 33 and 45 should be able to separate something cut into the LP vs the cart.
@Hans, It's this particular cart that is misbehaving, I have lots of pink noise LP's and this is just a curiosity at this point.
Dirt or scratches can't show up like that on an averaged FFT, those are too similar to be 100% coincidence.
Foolish me, but does this not appear to show a similar pattern to Scott's unexpected observation?
This is in the f domain, remember - it doesn't fit dirt/scratch events at all, and besides: why the so similar pattern?
Interested, yoda is. Hans seems to have confirmed Scott's odd result.
LD
I agree. Until just recently and davidsrsb's result I would have suggested level sensitive f response as the cause of difference between f sweep and pink noise results...……have to come up with something else now
LD
Yes, although slightly lower in frequency, I also had two blips in the "silent" channel between 2kHz and 20kHz, but not with the wild behaviour as in Scott's recording.
But we will need more data than just two recordings to build a theory.
And scratches may cause hf peaks that can be aliased back, depending on Fs and the quality of the anti-alias filter.
In that case, after averaging 8 spectra as in my image, peaks only get diminished in height but do not disappear completely.
Scott did not mention the used Fs and how many spectra he averaged so it's hard to judge the results, apart from the rather huge 9dB resonance around 13kHz.
And looking not only at spectra but also at the corresponding .wav files could also make sense.
So the question is again, does it make sense to make a few more recordings with differing Fs, different time length, different LP's, parts with a scratch in it ??
When you have concrete ideas, I'm there.
Hans
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