Monday, February 24, 2014

uncentered record wow

The discovery of the high wow measurement had me arguing with the seller, who agreed to take the turntable back (though for awhile I though he had changed his mind…leading to great angst).  I was getting mentally prepared for shipping LT-30 #1 back to the seller this week.

Then on Friday night after work (actually, the wee hours of Saturday morning) it occurred to me that some of the wow could be caused by the record being off center.  I recalled once reading that this could produce more wow than turntables themselves.

So I watched the Dr Feickert record playing.  I could clearly see the correlation between off center movement and the back and forth movement of the arm.  As the arm moved outward, the pitch went up, and vice versa.  I reversed the record 180 degrees and saw the exact same pattern.

So then I took the test disk and played on the Lenco L75.  Not only was the wow measurement not smaller, the flutter part (as measured by the IEC number of PlatterSpeed) was significantly worse.  Then my second LT-30 measured the same as the first.

Sometime on Saturday afternoon I emailed the seller and told him it looked like I was wrong, the turntable did not have excess wow at all.  I told him I'd check it out some more and if I couldn't find anything else wrong I'd close the eBay case on Monday.  I tried to leave the turntable on overnight (but turned it off without thinking) then just left the platter spinning for a couple of hours and repeated the measurement on Saturday afternoon.  Same measurement as before (it did not seem to be affected by having the turntable warmed up).  Then I watched the entire 3150 Hz track on the Dr Feickert record play.  No change from the beginning of the track to the end.  Not wanted to unnecessarily worry the seller any more, I closed the case on Saturday night.

Sometime on Saturday I re-discovered the page on off-center wow written by REG of The Absolute Sound.  This is worth reading a bunch of times, as I did.

Now I'm kicking myself because for the same price as all the turntable's I've purchased, I could have gotten a refurbished Nakamichi Dragon CT (computing turntable) which I saw listed at Audiogon.  That would make far more difference in measurable wow than any difference reasonably well working turntables and the very best.  It would leapfrog from the pitch stability of most turntables (which turns out to be about the same…simply due to off center wow) into 10 times closer to perfection.  If I really cared about pitch stability, and knew what I was doing, that's what I would have done (though I might have balked at the asking price of a refurbished CT, $3800).

Modern turntables have been pushing weighted wow and flutter down below 0.04%.  Meanwhile, the best you can do from a typical record, like the Dr Feickert test record for example, is about 0.12% or 0.16%.  The off center wow simply overwhelms any wow produced by nearly any turntable.  The raw number is even worse, I was seeing total pitch variation on the order of 0.8%, but the weighting filter used to create the weighted wow measurement drops that down to 0.12% on the basis that wow at 0.5Hz is less bothersome than wow at higher frequencies.

So why bother making or having a turntable with low wow?  REG points out the disconnect, turntable manufacturers know this problem…they have to take special measures (not using normal records) to measure wow, such as making a special painted platter to be measured optically.  And yet, nobody except Nakamichi has even tried to make off center wow reducing turntables.  Nakamichi, alas, didn't sell many of these incredible turntables, they likely lost a lot of money on the project, and thus a market for center wow eliminating turntables was never established.  People go on today ignoring the problem, comparing the wow of top turntables such as Gyrodec and SP 10, as if it matters when they both have wow 10 or 20 times lower than the off center wow of typical records.

So then why am I bothering with a speed stable (0.001%) SP 10 Mk2a when my records will have 0.8% recurring speed errors?

I am very disappointed by all this.  But meanwhile, I do have speculative explanations of why people have so easily ignored wow from off center records and meanwhile obsess over the trivial wow and flutter of most turntables.  The one obvious thing, of course, is that wow at 0.5Hz is indeed less audible than it would be at higher frequencies (and before going too much higher, we'd start calling it flutter).  I can hear the 0.5 Hz wow on a test signal, but it was hard to tell on actual music.  The second thing is that since off-center wow will occur on all turntables (except Nakamichi), people will tend to associate the sound with the record itself, rather than misperformance of the turntable.  We will simply never know how good our records would sound without the off center wow.  The third thing is that the off center wow modulates other wow components at higher frequencies, making THEM (or what we think they are) more audible.

As we can hear music below the noise floor, paradoxically it appears we can spectrum analyze very small wow components at higher frequencies even in the face of the large wow at 0.5Hz.

It would be even more paradoxical to believe that with all this wowing going on, we can hear tiny difference between turntables in their ability to correct the speed allegedly at the start of or after heavy groove modulation.  But I still think this is true.

I believe record would sound hugely better with off-centeredness lowered from about 2mm (typical) to 0.02.  And that center correction would reduce the apparent magnitude of higher frequency wow and flutter as well, and turntable speed correction effects, a huge win all around.  But most audiophiles including me have never heard this.

(I once attended a meeting where the Nakamichi turntables were being unveiled, and I recall the CT 1000 being played.  It was a noisy meeting and I suspect I wasn't paying enough attention to hear any huge difference.  So…Nakamichi's turntable failures are partly my fault as well.)

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