Posted by Steve King on 07/11/06 17:44

"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.
>
> 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

Great quote! To answer your question (and Rick's), no, I do not think that
drop-outs disappeared with the advent of digital. I mentioned in a thread a
few weeks ago that I had had a first encounter with drop out (after four
years of professional use of DV). However, Rick's acceptance of drop-out as
generational loss is akin to accepting as generational loss the errors that
might result from a house-sized meteor falling on the DV deck during
transfer, in other words, anything that causes errors. Your comments about
the DV standard allowing for bit-errors is over my head. Do all DV tapes
have bit errors? If so, and if they accumulate with each transfer, then I
guess that would be generational loss. Oh, and is computer tape as used in
backing up the most valuable data on the planet different from DV tape? Or,
are we really interested any more? ;-)

Steve King

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