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Posted by Toby on 07/13/06 02:27
"Richard Crowley" <richard.7.crowley@intel.com> wrote in message
news:e90ke7$e21$1@news01.intel.com...
> "Steve King" wrote ...
>> "Rick Merrill" wrote ...
>
>>> There is potential generational loss in dup of DV25 tape, but not if the
>>> data has been stored in files (on disk).
>>
>> Why would that be?
>
> Because of the difference in ECC between computer media and
> audio/video media. Consider that if you fill an audio CD with music
> tracks, you cannot fit the WAV files they came from on a data CD
> of equivalent size. That is because the ECC requirements for computer
> data are significantly more stringent than for audio/video data. The
> checksums, etc. that are used in "Orange Book" data discs take
> more space than the minimal ECC used in "Red Book" audio CDs.
>
> Note that the high-end manufacturers of commercial pressed CDs
> (and DVDs) will not accept a master recording on an optical media
> disc (CD-R or DVD-R) because of the error rates. They will accept
> master recordings only as data files to ensure bit-perfect source
> material.
>
> Even a single bit error in a computer file is unacceptable. OTOH,
> single-bit errors in audio and video happen many times per second
> and we never notice because of the nature of the data lends itself
> well to error mitigation by extrapolation. You can't extrapolate what
> the value of an unknown byte would be in a data file, but it is easy
> for audio or video. It is quite likely that you have never heard a
> bit-perfect playback of an audio CD, for example, even a brand-
> new disc out of the box.
As an interesting aside, I recently bought a digital slr, and after some
repair work was horrified to find three bright white dead pixels. To make a
long story short, I brought the camera back, and within the hour they had
remapped the pixels to the value of their neighbors. It was pointed out to
me that when a chip is manufactured it probably has hundreds, if not
thousands of such dead pixels, which are remapped at the factory and no one
is the wiser. Likewise huge patches on the platens of HDDs are unusable, and
those bad sectors are simply skipped, with the user none the wiser except to
wonder why his 100 Gb disk only shows up at 93 gigs.
It's totally ludicrous to believe that the same is not happening on DV
tapes. One of the great advantages to DV is the cost of head replacement.
Analog heads were fine pieces of precision workmanship, with price tags to
match. They can slam digital heads out for a fraction of the price, since
the tolerances are so much greater for reading and writing 1s and 0s. And of
course, you have that itty bitty little tape running at such a slow speed.
You don't think you need good error correction? LOL!
Toby
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