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#241
A swept carrier?

I don't think that would be very workable as you are trying to pick up speed variations (due to whatever mechanism). The easiest signal to show that would be a constant tone because aberrations will stick out like a sore thumb. Given that we already have a standard test signal and equipment specially developed for this work, why not just use that as we have been doing since the first test LP was pressed?

-Chris
 
#242
If head shell motion and damping affects speed stability, a damped (Proper Material ? fluid ?) and stiff unibody well damped tonearm will solve most of the problem. Am I thinking right ? Any practical example of such tonearm/s ?

As we go for precise high quality vinyl pressing where speed stability measurements will be very low, and if a tone has inherent speed variation while pressing master how can we differentiate the two ?
Thanks and regards.
 
#244
The issue I have with analouge source material like an LP is that my 4-way speaker system is partly digital for the sub and midwoofer. The only passive crossover I use is 2 order, for mids and tweeter. Below 440Hz I have a sub and two JBL woofers. I have not found a good way to make a passive crossover for the crossover points 20-80Hz and 80-440Hz, without huge crossover components that doesn't sound good. But I would love to try true analog one day.
 
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#245
The fact that you have a digital crossover doesn't have any bearing on a test LP to optimise turntable though. Fairly soon I will be doing all cross-over duties in the digital domain. Doesn't mean I can't get the best out of my turntable!
 
#246
billshurv said:
The fact that you have a digital crossover doesn't have any bearing on a test LP to optimise turntable though. Fairly soon I will be doing all cross-over duties in the digital domain. Doesn't mean I can't get the best out of my turntable!
Click to expand...

So your idea of a pleasant listening experience is to convert the material from analog (LP) to digital (DAC+digital crossover) and then analog again (amp+speakers)?

I just don't see the point in using an LP with a speaker system with a digital crossover. Digital source material today probably uses better DACs than I would when converting the signal from the LP. And even if I would be able to afford a better DAC, the extra conversion would reduce the quality anyway.
 
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#249
diyrayk said:
This thread started as an offshoot from the Turntable Speed Stability thread, but the proposed tests so far seem to be steady state signals, many of which can be found on discs that are currently available. The ‘TSS’ thread Turntable speed stabilty found that unwanted headshell motion can cause significant FM/pitch variation due to stylus scrubbing. These effects are influenced by tonearm geometry and tonearm damping, so that the measured stability of the signal output from the cartridge can be affected as much by tonearm characteristics as by the turntable drive characteristics.

I propose a dynamic test signal that I’ve not seen on any test discs. Groove modulation increases stylus drag. We know that stylus drag force applied to a tonearm with an offset angle causes skating. Skating force, and the stylus deflection it causes, is not constant. It varies, and it can vary dynamically, depending on groove modulation level, or amplitude. If the groove modulation/amplitude varies at a rate near the mass/compliance resonance frequency, the varying stylus drag could stimulate headshell motion at the mass/compliance resonance frequency. The attendant stylus scrubbing would cause dynamic FM/pitch variation of the signal which would look like turntable speed instability, but the effect would be attributed to the tonearm characteristics and not necessarily associated with the turntable drive. The band would be a carrier of suitable frequency, perhaps 1000 or 3000 Hz, and swept from 1 to 20 Hz or so. Odd as it may seem, such a signal could stimulate mass/compliance resonance even though it does not contain any low frequencies itself. The next band would be the same carrier signal, but unmodulated, which should theoretically yield a steady state condition without the influence of measured instability due to dynamic tonearm effects. In a perfect world, the measured instability observed from the two test bands would be the same. Comparing the diferences of the results from these two bands could help ferret out the relative contributions of tonearm dynamic behavior vs. turntable drive instability??

Ray K
Click to expand...
Yes. Another method might be to mix (by addition) a sweep of 1 to 20Hz or so with a ~3kHz carrier tone?

Further, one could add a ~3kHz carrier tone to normal programme material, to directly investigate effects of programme material modulation on speed stability..............interesting? FFT/Hilbert transforms being wonderful things, the carrier's spectral peak would always be detectable.

LD
 
#250
luckythedog said:
Further, one could add a ~3kHz carrier tone to normal programme material, to directly investigate effects of programme material modulation on speed stability..............interesting? FFT/Hilbert transforms being wonderful things, the carrier's spectral peak would always be detectable.
Click to expand...

The first is fine IMO but I would vette the second via simulation because it could be tricky.
 
#253
A quick simulation with 3150Hz test tone@-20dB ref programme peak was eventually fine, but required a narrow deep notch-out in programme eq to avoid the carrier and sidebands which seems not much of a compromise in the scheme of things.

I think this might make an excellent and interesting test of programme material induced cart/arm stability.

I'll post test files and results on this thread, I think, since it relates to synthesis of a test file. Might a take a day or two, I'm a bit busy right now......

Interesting stuff.

LD
 
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#255
Yes it would. Scott and i have discussed this, and don't see it as a huge problem, but it will likely remain a question in people's minds, so should be addressed.

I did propose a signal that would allow direct, optical observation of lathe speed and also give an idea of stability. Other ideas are welcome. There may be a standard test for this already, but I haven't sound mention of it anywhere.
 
#257
Pano said:
Yes it would. Scott and i have discussed this, and don't see it as a huge problem, but it will likely remain a question in people's minds, so should be addressed.
Click to expand...

I ran into this last night, the 1kHz reference tones that start each sweep on the same LP had very different FM spectra, one in particular was very bad. Without changing anything but moving the belt to the 45rpm position the results were the same just translated 1.35 up in frequency. Note also playing tracks at different speeds distorts the RIAA, digital EQ would help here a lot since no one would want to build custom RIAA's.

This was very perplexing since it was my CBS STR130. I could only conclude that it was actually on the LP. Does anyone know the production history, these were late copies bought from Old Colony circa 1980?
 
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