Posted by Richard Crowley on 01/12/71 11:52

"PTravel" wrote ...
> "Martin Heffels" wrote ...
>> Data drop-out is the equivalent of generation-loss in digital
>> duplication.
>
> No, it isn't. Generational loss is inevitable and progressive when duping
> analog video. Drop out is caused by physical failure of the tape and is
> neither inevitable nor likely for D-25.

Small, correctable, dropouts likely occur more frequently in
D-25 than you think. But since they are automatically detected
and corrected, you don't know they are happening. The only
time we *see* it is when it gets so bad, the ECC can't handle it.

> This thread appears to have been an old one that someone decided to
> resurrect.

It appears to have started only two days ago. (8-Jul)

> The question appears to be, "Is there generational loss when duping
> digital video?" The answer is, "No," not, "Yes if you do it 100 times, as
> another poster has claimed."

Well, there is *NO* generational loss when copying a digital
data. However some digital media have less robust ECC than
others. Data media (hard drives, floppies, computer backup
tape, CD-ROM, DVD-ROM, etc.) use very robust ECC
mechanisms which ensure 99.999999% dependable bit-for bit
reliability. OTOH, digital audio/video media formats (like audio
CDs, DVDs, DV tape, etc.) use less robust ECC because a
few bits of error here or there don't mean the same thing in an
audio or video signal that they do in a computer executable file
or your bank's accounting data.

Technicaly, you could make a valid argument for either "yes"
or "no" as an answer to answer this question.

> There is no recompression at all when making a digital dupe -- whether
> D-25, mpeg, divx or whatever,

Absolutely, and one of the huge advantages of digital over
analog.

> as when any digital data, you can copy the file ad infinitum with no loss
> whatsoever.

Not as valid to try to apply computer-type data handling
reliability to digital audio/video media. They use different
levels of ECC for their different requirements and their
different economic markets, etc.

> By "loss," I assume you may "drop out." Because drop out is caused by a
> physical failure of the tape, you're not going to lose just one pixel on
> one frame -- drop out on digital tape is rather obvious because it effecs
> a block of data.

But frequently that block of data can be completely and
accurately reconstituted by the ECC. This likely happens
hundreds of times an hour in what we think are "perfect"
DV-25 tape playbacks.

> I use an old TRV-20 consumer camcorder for transferring my miniDV to my
> computer (I fried the 1394 port on my VX2000 a couple of yearas ago).
> This camera puts out what is one the tape, and doesn't detect or fix drop
> outs.

It most certainly does both detect and fix dropouts.
Else it wouldn't even work. I suspect that all of you who
think that digital is so pristine would be horrified if you had
a peek "under the hood". :-) Take a look at a service manual
for any DV camcorder if you need to be reminded of the
analog nature of tape (even digital tape).

I work side-by side with hundreds of engineers who design the
most advanced and complex digital chips in our known universe.
But almost none of them think in the "digital" domain. Their jobs
involve dealing with the real analog world and making it look
"digital" at the interface where the pins connect to the motherboard.
The people who design magnetic and optical digital media have
the same task of making the fundamentaly analog world behave
like "digital".

> Sorry, you're wrong. Hard disks use ECC, just like tape.

They both use ECC, but the ECC used on hard drives is much
more robust and reliable than what is used on DV tape. (And it
takes more space away from storage the capacity). The expectation
for data is that you will get one uncorrectable error in several
trillion bits whereas most of us likely have seen and/or heard
uncorrectable errors in digital audio/video media in recent memory.

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