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Posted by Richard Crowley on 07/11/06 16:42
"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.
While a DV stream is frozen in a DV-AVI file on a computer, it is
guaranteed bit-perfect handling, just as any computer file would enjoy.
But when it is recorded on a tape, it is subject to the lesser standards
of DV data handling. Fortunately the engineers who designed the DV
standard made excellent tradeoffs between data integrity and cost vs.
benefit for tape size/thickness, running time, cost to manufacture, etc.
etc. etc. I am completely satisfied with the tradeoffs they made in
the design of the DV tape format. It doesn't trouble me in the least
that it is not bit-perfect. But I wouldn't expect that a 20th generation
DV tape dub would be completely free of visible errors, either.
>Are you considering what was called 'drop-out' in analogue days?
Do you think that dropouts disappeared with the advent of digital?
They are just as much a factor as they ever were. But one of the
great advantages of digital is that you can much more easily detect
a problem and fix it than you could with analog.
> If so, I would not consider that 'generational loss', which seems to me
> to be more concerned with the noise floor and
> frequency response limitations of analogue tape. Data files
> stored on disks are also susceptible to imperfections in the media, which
> might be compared to tape drop out.
Multi-generation problems didn't disappear with digital media
like DV, the just change nature somewhat.
But this whole discussion has become enormously overblown
and reminds me of one of my favorite quotes from a great TV
show ("Sports Night"): "I gotta tell ya, at this point the length
of this conversation is way out of proportion to my interest in it."
- Dan Rydell http://us.imdb.com/title/tt0165961/quotes
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