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In the Forum: Analog Playback
In the Thread: Turntable speed analysis.

Post Subject: Understanding the reasons....Posted by Romy the Cat on: 6/11/2012

N-set wrote:
There is a certain analogy between THD number and Wow&Flutter number: bare THD tells you very little, if anything at all, about the amp, one has to dig into that number deeper and see a detailed spectrum behind it.

Actually there is not. When I was taking “irregularity lower than 0.1%” I did not mean THD but the rotational irregularity, or Wow&Flutter. I am not familiar with TT Wow&Flutter but in my past I dealt a LOT with reel tape and I know that if we are beyond 0.1% then we are out of dander.

N-set wrote:
I'm not sure if Paul R gave you more output than what he wrote on the PF, but I think neither of us really gave a solid interpretation as it is difficult at this moment: too little experience with the tool. One clearly sees a regular waviness, there is something happening approx 16 times per revolution. This may be induced by the motor and/or amplified by themotor-belt interaction (is your belt stiff or soft?).

This is the whole point – even if we do see the problem we still have no knowledge where this problem came from and is responsible for it. Did the record was cut properly. Did they cut the whole on exact middle? Did the platter during the record cutting had any speed regularity? Oh, this is a huge question and a big work to be done: correlate measurements to the sonic results. As I see it at this moment the tool is still in its teething fase, identifying merely some "hardware" mechanics in the plots. This is needed to learn the tool, but I hope with time the hard work of correlating with the sound will start (again an analogy to the advent of spectrum analyzers in amp analysis is in order IMHO). As you imagine a time (and a good will of the community!) is needed to establish enough statistics. The statements "irregularities below 0.X% are not auditable" I'd treat rather carefully, just like parallel statements made thoughout the years that THD below X% is not auditable... I disagree. The THD are deterrent from W&F as W&F are pretty much liner distortion existing in nature. In THD the order of the harmonics is important and the reason that creates the distortion is important. In case of Wow&Flutter the reason is NOT important but only the fact.

N-set wrote:
I do not 100% agree that comparing different topologies is meaningles. Quite to the opposite: instead of intellectual fantasy arguments (like invoking "laws of physics" and other crap), one can measure different topologies and see how they differ between each other in reaching what seems at the moment to be the objective: a constant rotation of the platter. Same with e.g. different amp topologies: why wouldn't it make sense to spectrum analyze a PP amp and a SET and compare? Obviously, what you propose in the second part has already been going on: perform a different action on the TT and then see the results,both measured and sonical. People try different PSU, oils, dampings etc etc.

What I was trying to say was that comparing the same topology give an explanation WHY the analyses looks like it looks. If you have a TT with analyses done on a given record then you can run the same analyses again but juts for instance loose the belt tension or supplying more air pressure in platter suspension. This single change would give an idea of how the analyses be different in case of one single change was done. Doing it for loooooooong time we might understand the reasons and predict what was responsible for this or that bad analyses.

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