Re: DV: digital vs. analog dubs


"Martin Heffels" <youwishyouwouldknow@xxxxxxxxxxxxxxx> wrote in message
news:b2p5b290jrdg8fs9ameeg1l27gd77vmasi@xxxxxxxxxx
On Mon, 10 Jul 2006 13:22:17 -0700, "PTravel" <ptravel@xxxxxxxxxxxx>
wrote:

[...]
That's still apples and oranges. I didn't say that this kind of
"correction" isn't done. I said that it's extremely rare and the kind of
common "drop out" that you've been discussing is fixed by ECC in such a
way
that no data is lost.

Google a bit on "bit error rate", and hop into the hits at the patent
office.

The patent office? Sorry, but people can put whatever they want in a
patent -- the USPTO doesn't vet patent specifications for accuracy.
Moreover, the question isn't "bit error rate," but "uncorrectable error rate
as applied to dv tape."

You'll find some interesting documents about designs of tapes, and
how reducing it's size increased the BER above accepteable levels. It says
to me that they occur much more than we think.

It says to me that inventors say whatever they want in a patent spec and,
because of the "useful" requirement for issuing a patent, they will say just
about anything to demonstrate the need for an invention. I may be a
dilettante about video, but patents I know . . . extremely well.

It is very hard though to find any sensible figures on it.

Well, that's odd. If generational loss for DV copying was an issue, I'd
expect to see lots written about it, just as I see lots written about
generational loss for analog video. Instead, all I can find is sources that
say there is no generational loss for video copying.

I have read an
article about it in an SMPTE-magazine, but their magazines are not online

SMPTE is, of course, a reliable source of data. Did the article say that
copying digital video tape commonly results in data loss due to
uncorrectable errors?

:-(

Here's some links with some info/tables/test-results:
http://www.pmdmagnetics.com/displayfile.asp?id=48140
http://www.urbanfox.tv/articles/formats/fm3test.htm#generation

This one quotes some figures:
http://www.creativevideo.co.uk/public/pdf/sony_dvcam_2005-6_inc_xdcam.pdf
DV: 100 counts/min, DVCAM: 50 counts/min

You see above. You understand how ECC works, and you also understand that
ECC is capable of correcting small errors without data loss.

Yes.



We're talking apples and oranges here. On the one hand, there's
everyone's
DV deck that can invent data if it's missing,

There is no deck which "invents" missing data. They interpolate, based
on
what is there. Inventing means coming-up with something completely new
which didn't exist before.

Now who's arguing semantics? Interpolated data is data that is different
than what was actually recorded, hence it's invented.

No it is not. It is based on something which exists, and most likely to be
correct. If you see nasty blocks, that is data which is invented!

[...]
Doesn't matter. The kind of gross data correction that results in
"interpolation" of data is extremely rare.

You just assume this, because you have never seen it.

[...]
No, I didn't. I meant that analogue waveforms get smoothed in an analogue
copy, that noise is introduced, etc. Impedence mismatch is one way that
an
analogue signal can be degraded, but it's hardly the only way.

Understood. Indeed, not the only way.

[...]
That's right. How often do you think miniDV experiences drop out so
severe
that it results in an uncorrectable error?

Well, watching tv, I see digital drop-outs quite a lot, from stuff
recorded
on tape. On a personal level, I once had this bad batch of DVCAM-tapes,
which had a drop-out every 5 seconds. On my personal material maybe once
every 100 tapes (discounting the older stuff shot on LP).

[...]
If it's been error-corrected, it doesn't matter, because a bit-for-bit
copy
results and there is no generational loss. If it has been concealed, it
does matter but I don't believe that happens often enough (with proper
technique -- I'm sure you can induce significant drop out if you put your
mind to it) to be a consideration when duping digital data.

Well I'm glad you believe us now that there is a difference in
error-correction methods.

I don't think it's pristine. I do think that the ECC for D-25 is
sufficiently robust so that, by using quality tapes only once, and
maintaining my camcorder, I can produce digital transfers to and from
the
computer without any dataloss.

Yes and no.

In my case, yes and yes, as well as in the case of others who have posted
about drop out to this newsgroup, e.g. drop out reported due to a bad tape
batch, etc.

Agreed, Above mentioned will avoid the risk of drop-outs tremendously.
Another important factor to maintain not running into drop-outs, is to
store the tapes properly.

My capture software can stop on error -- never had it happen, though.

That's the advantage of just editing your own material :-)

cheers

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


.

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