Posted by PTravel on 01/12/35 11:52

"Martin Heffels" <youwishyouwouldknow@nottellinya.com> wrote in message
news:lb74b252qk6im2fbcukpb02do91k8qrgga@4ax.com...
> On 9 Jul 2006 17:35:07 -0700, ptravel@travelersvideo.com wrote:
>
>>Absolutely not. There is a slight possibility of data drop out, as
>>there is with any digital storage medium (and that possiblity is
>>extremely rare). There is, however, no generational loss.
>
> 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.


> Of course, the laywer that you are, we are going to have a semantics
> battle
> about this :-)

Yes, whenever you're wrong, blame it on the fact that I'm a lawyer.

> But I use it in terms of popular semantics, which is not
> always strictly correct for those who follow the letter of the law :-)

It's inaccurate and misleading. This thread appears to have been an old one
that someone decided to resurrect. 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."


>
>>
>>>
>>> >> Doubt it. I do remember one test involving multiple generations of
>>> >> recompression of DV footage which claimed degradation after about 18
>>> >> generations, but you shouldn't see serious issues when making digital
>>> >> copies. You're likely to have the odd dropout on the tape, but
>>> >> otherwise the general quality should be fine.
>>> >
>>> >You're correct that the there will be no generation loss. However,
>>> >drop-out
>>> >from digital video tape is very, very rare.
>>>
>>> Not correct. This solely depends on the quality of the codecs used.
>>
>>Look up the meaning of drop out. It has nothing to do with codecs.
>
> We were talking about generation-loss from multiple recompression.

There is no recompression at all when making a digital dupe -- whether D-25,
mpeg, divx or whatever, as when any digital data, you can copy the file ad
infinitum with no loss whatsoever.

> A couple
> of years ago I tried this with the MS-DV25 codec, and after the second
> recompression, you already saw some serious loss in quality.

The thread asked about digital dupes, not recompression. Obviously,
recompression with a lossy codec will result in generational loss.

> The MS-DV25
> codec has improved tremendously by now, but it still can't hold up a
> candle
> to the ones of Canopus and Matrox.
>
>>
>>> And
>>> then it can quickly add up. The standard MS-codec is still of lower
>>> quality, and won't keep up with those 18 generations at all.
>>
>>Absolute nonsense. You can dupe a D-25 tape 18 times and the 18th copy
>>will be identical to the first.
>
> Again, stick to the topic of the paragraph :-)

I am. Drop-out within 18 dupes means a drop out rate of 5.5%. Unless
you're storing your camera in sand, you're not going to see drop out rates
remotely approaching that. Do you get 5.5% data loss from drop outs for
your video?

> But you're wrong anyway. You
> won't notice the loss at all, but it's still there.

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.

> If you use a decent
> deck like a DSR1800 to make those dupes, you can see on the front of the
> deck, the quality of the signal going out via a green/red bar. If the bar
> shoots into red, that means that digital mumbo-jumbo will be applied so
> you
> won't notice the drop-outs. As someone else also mentioned, copying blocks
> from adjacent frames for instance.

I don't use a DSR1800 deck (though it would be nice to have one). 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.

>
>>Yeah -- one is tape, one isn't. However, the statement stands: error
>>correction is used for both media, and the chances of drop out are
>>miniscule on either.
>
> No. A hard-disk moves data to another block if it thinks the block is
> corrupt. But there is no chance that the operating system knows if the
> data
> is correct. It can only make an educated guess.
> With tape there are some extra bits and pieces send with the data which
> can
> repair the data a bit. But sometimes this goes wrong as well.

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

>
> cheers
>
> -martin-
> --
> "If he can he'll smile 'cos he's a Royal Crocodile."

[Back to original message]