Vinyl Asylum

Jitter

124.168.55.168

In Reply to: RE: But Mark, the round dot looks cooler! posted by powermatic on May 13, 2008 at 07:29:36

Using a round dot decreases the rise time of the transitions from dark to light and back. Since the signal is noisy the decreased slope increases the variation in the point where the device switches state, this is analogous to jitter in a DAC.

I don't think the effect will be measurable, it would have to move by about 1mm to make a 1 part per thousand difference (the circumference of the platter being roughly 1 metre).

On the other hand if attempted to improve precision by placing multiple dots the problem is compounded by the shortening of the space: 10 dots would be spaced roughly 100mm apart, to get 1/10,000 accuracy they would have to be within 10 um of the correct spacing, that's less than half a thou; tricky but not impossible with the right tools. For 100 dots and 1/100,000 the spacing would be 100 nm which is entirely impracticable.

On the other hand measurements to much greater precision than that are possible with a single dot and an oscilloscope but I think I'm safe in assuming no-one cares.
Mark Kelly

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