Posted by Martin Heffels on 01/12/61 11:52

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.
Of course, the laywer that you are, we are going to have a semantics battle
about this :-) But I use it in terms of popular semantics, which is not
always strictly correct for those who follow the letter of the law :-)

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

>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.

cheers

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

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