The reason why this would be important for coming up with a theoretically perfect dump is that many discs these days have minor dropouts that would be quite difficult indeed to correct manually by merging together captures of multiple different examples of the same disc.
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In principle, knowing whether a single sample of the analog data was "good" or not would enable a sufficiently dedicated person to construct a capture with *zero* horizontal streaking or other artifacting due progressive rot.
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Vastauksena käyttäjille @TheMogMiner ja @aaronsgiles
If you digitize a vinyl LP or an audio cassette 100 times, you will get 100 different sets of digital data, and no one of them, nor any composite you can make from them, are "correct". This is true for all analog recording systems.
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That's basic information theory, not something I'm making up. But I'll shut up now.
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Vastauksena käyttäjille @brouhaha ja @aaronsgiles
No, they're not "correct" in the literal sense. I don't debate that. But if you have two captures of two tapes, with both having had the mylar physically damaged in different spots, then shouldn't it be viable to splice the two together to form a capture better than either one?
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Vastauksena käyttäjille @TheMogMiner ja @aaronsgiles
Yes. That can be done without sampling at the optical pickup. The optical pickup gives you no additional information that's useful for that.
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The optical pickup can't magically tell whether a bit of oxidation of the aluminum or a scratch on the surface has made a pit look more like a land. It can only tell you if the laser is significantly out of focus, which only happens with severe laser rot, or broken player.
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Vastauksena käyttäjille @brouhaha ja @aaronsgiles
This is a really great point, and thank you for making it. It actually gives a technical reason for why it's unnecessary rather than resorting to "I know more about information theory than you", and it makes perfect sense. So, thank you.
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Having said that, it is possible to capture the VBI data since it's just a property of the video signal, simply one that most capture software cuts off before displaying it to the user. In fact, I believe the Cube Quest dump in MAME that Aaron did contains that data.
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It's just that it was captured with an ancient (by today's standards) capture card using hacked drivers that, I seem to recall, required Win 9x. Based on the information you're providing, it sounds like the ideal solution would be to find an equivalent method on a modern OS, yes?
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Pretty much just find a capture device that can have its software/drivers modified to extend the region of the signal which is captured to include VBI data, manually merge captures to eliminate any bad regions of the disc, and call it a day.
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Vastauksena käyttäjille @TheMogMiner ja @aaronsgiles
Possibly rather than using a device made specifically for capturing video, a general high-speed data acquisition (ADC) board could be used.
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Vastauksena käyttäjille @brouhaha ja @aaronsgiles
That's a pretty solid idea, as it would eliminate any possible sources of noise from a capture card trying to do any sort of weird post-processing or upscaling. And given an LD player of high enough quality, there shouldn't be much appreciable noise added to what's on the disc.
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