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Posted by PTravel on 10/05/96 11:52
"Richard Crowley" <richard.7.crowley@intel.com> wrote in message
news:e8ut9v$hkr$1@news01.intel.com...
> "PTravel" wrote ...
>> I'm just looking at the resulting copy. I take a black box approach to
>> these things, i.e. if the output is the same as the input, it doesn't
>> matter to me what happens inside the black box to make it so.
>
> And that is my attitude as well. DV is more than adequate for all the
> different kinds of video production I do as long as I stay within the
> parameters.
>
>> In this discussion, if I wind up with a bit-for-bit accurate copy, it
>> doesn't matter to me whether the ECC guessed, used psychic prediction, or
>> had employed a time machine -- a bit-for-bit accurate
>> copy means no generational loss.
>
> Perhaps you don't understand the difference between real data
> *correction* (via ECC) and migitagion/extrapolation. The former is
> bit-perfect, and the latter takes advantage of the nature of the data
> to make educated guesses. Most of us (me included) won't know
> or care whether the data is bit-perfect as long as it is good enough,
> and that is the nature of DV (and audio CD, and DVD, etc.)
I do understand the difference, but we keep talking past each other. "real
data 'correction'" results in a bit-for-bit perfect copy. Mitigation
doesn't. My question was how often does mitigation occur? No one has
answered that.
>
>> We're not disagreeing about that. My question is this: how often, in
>> duping from a DV tape, are there data failures that cannot be corrected
>> exactly as they are for computer files? I've never heard anything other
>> than, "so rarely that it's not a concern."
>
> If everything is optimal (equipment within interchange adjustment,
> clean, not worn-out, etc.) then it very likely is "so rarely that it's not
> a concern".
Which is what I've been saying.
> But that is not the same as "bit perfect". If comptuer
> data had the same uncorrectable error rate as audio and video
> digital data, we would have abandoned using computers for anything
> but casual gaming.
Corrected data that is not mitigated in the sense that you've used the term
is bit-for-bit accurate.
>
>> All I know about audio CDs is that my computer employs error correction
>> when it reads them.
>
> Every CD player down to the $15 one from Wal-Mart employs
> error correction when it reads them. They would not be readable
> without sophisticated ECC.
>
>> However, that's still audio CDs -- I'm asking about digital video tape.
>
> Same thing happens to all digital media, whether magnetic or
> optical. Dunno whether you had seen this before?
> http://www.adamwilt.com/pix-defects.html
Yep. Good examples of drop out that results in uncorrectable errors. I've
never, ever had that happen, and I've not heard reports from anyone else
saying its anything but highly unusual.
>
>> I never said it was zero, as people in this ng have reported the
>> occassional data-losing dropout. Heck, cosmic rays could probably cause
>> it, but how often do cosmic rays effect video playback (answer: not
>> often).
>
> When you used the terms (previously in the message I am replying to)
> "if the output is the same as the input", and "bit-for-bit accurate copy",
> I took that to mean "zero".
The question remains how often this happens. If it is so rare that it
happens once in 10,000 hours then, for all intents and purposes, it's zero.
> If we agree that there is a non-zero rate
> of uncorrected errors, then we also agree that there is some non-zero
> "generation loss" (or whatever you want to call it).
There is generation loss only if an error occurs, and it depends on the
probability of this happening. Any duped analogue signal will exhibit
generation loss. Any duped digital signal will not, unless one of these
errors occur. If it does not, then there is no generation loss at all.
>
> If you want to believe that DV tape technology is bit-perfect, I don't
> see any reason to try to persuade you otherwise. I'm sure that the
> engineers who designed the system dearly wish it was as simple as
> your concept of it.
Then tell me what the uncorrectable error rate is for DV tape.
>
> In any case I will continue to use DV tape technology without
> regard to its <100% bit-perfect accuracy. Since I never intend
> to abuse the format by doing anything past 2nd or 3rd generation
> tape-to-tape dubbing, my only concern is something physiclly
> happening to the equipment (like when my DSR-300 lost one of
> its tape guides). Regardless of how much we know about the
> internals, we both (and millions of other users)
>
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