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Posted by Toby on 07/14/06 08:51
snip
>>>>
>>>> "DVCAM tape has a 50% lower dropout rate vs DV resulting in a four- to
>>>> five-fold improvement in the error rate margin, which yields a better
>>>> picture."
>>>
>>> Irrelevant (and marketing).
>>
>> Why is this more irrelevant than the Adobe claim, which is also
>> marketing?
>
> They're both irrelevant. The only relevance of the Adobe claim is that I
> will accept it before an unsupported assertion by a Usenet poster because
> Adobe is on the hook for FTC violations if it's wrong.
To each his own. I'm not the lawyer, but I would guess that there are
literally thousands of marketing claims which are in essence or in substance
untrue and which could put their companies on the hook for FTC violations,
which doesn't stop the claims. You'll remember that this whole thread
started because the OP was wondering about the claim that firewire dubs are
"virtually lossless", and why always the "virtually"? So maybe some
companies are more careful in their claims than Adobe.
>
>>
>>>
>>>>
>>>> So somebody is lying, is it Adobe or Sony?
>>>
>>> "Better picture" is one of those subjective terms that are legally
>>> termed "puffery." However, Sony's material could easily be interpretted
>>> as saying, essentially, DVCAM is better than DV because the 50% lower
>>> drop out rate means one mitigated error per 1332 hours of video, versus
>>> one mitigated error per 666.
>>
>> So Sony is lying? Or is it Adobe?
>
> I don't know. Neither do you.
But the point is, that even with one unrecoverable error every 1332 hours,
DV isn't loseless as you and Adobe claim. Virtually lossless, yes, lossless,
no.
>
>>
>>>
>>> Hard evidence. Not speculation.
>>
>> Where is the hard evidence on the Adobe claim?
>
> There isn't any. Context is everything -- I've explained the context in
> which the Adobe claim was relevant.
Lawyers make my head spin.
>
>>
>>>
>>>>
>>>> Here's a quote that perhaps expands on that theme:
>>>>
>>>> "Finally, banding or striping of the image occurs when one head of the
>>>> two on the scanner is clogged or otherwise unable to recover data. The
>>>> image will show 10 horizontal bands (12 in PAL countries), with every
>>>> other band showing a "live" picture and the alternate bands showing a
>>>> freeze frame of a previous image or of no image at all (or, at least in
>>>> the case of the JVC GR-DV1u, a black-and-white checkerboard, which the
>>>> frame buffers appear to be initialized with). Most often this is due
>>>> to a head clog, and cleaning the heads using a standard manufacturer's
>>>> head cleaning tape is all that's required. It can also be caused by
>>>> tape damage, or by a defective tape. If head cleaning and changing the
>>>> tape used don't solve it, you may have a dead head or head preamp;
>>>> service will be required.
>>>>
>>>> This sort of banding dropout occurs fairly often; about once per DV
>>>> tape in my experience.
>>>
>>> You can't be serious. I've never experienced that kind of banding
>>> dropout. Do y ou keep your equipment clean? Do you mix dry and wet lube
>>> tapes?
>>
>> This is a quote from a professional. Note that he says: "banding or
>> striping of the image occurs when one head of the two on the scanner is
>> clogged or *otherwise unable to recover data*."(emphasis mine). And
>> clogging isn't always an issue due to inadequate cleaning. Ever hear of
>> oxide flaking? It happens routinely even on the best tapes.
>
> I didn't say it was the result of inadequate cleaning. It can result from
> over-reusing tapes, from a bad batch of tape, from humidity and other
> environmental conditions, etc. Notwithstanding what the professional,
> I've never seen it with my only-reasonably-well-cared-for prosumer
> camcorder. Of course, I don't reuse tapes, stick to one band, and don't
> use it in harsh conditions.
Nor do you shoot and edit video day in day out, week after week, I presume.
>
>>
>> Take note that a figure for this kind of unrecoverable error is given in
>> the last line, and it is more than an order of magnitude larger than your
>> contrived one.
>
> I didn't contrive it -- I'm merely repeating the guestimates that have
> been ventured in this newsgroup. My number is pure fiction. The number
> in the article doesn't comport with my own experience. Both numbers are
> anecdotal and not based on hard data.
How much harder does it have to be? The man experiences dropouts which are
unrecoverable, approximately one per tape, and which cause banding. Do we
need a notary there to certify his claims?
>
>>
>>>
>>>
>>>> Usually it isn't even noticeable -- a single frame of banding due to a
>>>> momentarily clogged head won't be visible unless there's motion in the
>>>> scene to show off the frozen stripes.
>>>
>>> Since I rarely shoot with a tripod, my video is always moving.
>>
>> Irrelevant.
>
> Hardly irrelevant. You: it won't be visible unless there's motion. Me:
> in my videos, there's always motion, yet I've never seen it.
However whether you see it or not, if there are unrecoverable errors
resulting in banding, there is data loss, and isn't that the point? If your
wife is cuckolding you behind your back and you never find out about it,
does that mean that you are not being cuckolded?
>
>> It means that there is lost data due to dropouts, hence the ECC is not
>> as perfect as you seem to so desperately want to believe.
>
> Then why haven't I experienced it?
Either because you don't know what to look for, you haven't shot and looked
at enough tape, or it hasn't happened to you. Have you ever done those
newspaper time-wasters: find the thirty differences between these two
pictures? Many are obvious only after you've really searched for them
repeatedly.
>
>>
>>>
>>>> Have a look through your old tapes frame by frame (on a slow day, of
>>>> course!) and you might be surprised how often you'll be able to find a
>>>> single, subtly banded frame.
>>>
>>> I don't go through my video frame by frame, but I do look at an awful
>>> lot of single frames in the process of editing a project. Never seen
>>> it.
>>
>> Which means that it doesn't exist?
>
> Nope. It means that my experience is contrary to the anonymous author of
> your article. I'll trust my own eyes.
>
>> And BTW, how many is "an awful lot"? Just for reference, there are
>> roughly 30 frames/sec, which translates into approximately 108,000 frames
>> on a 60 min. tape. Would you say that generally you carefully view 1% of
>> all frames shot? 10%? Give me a figure here...
>
> 1 or 2% is probably fair, though I don't "carefully view" each frame.
> However, I do view them carefully enough to note any errors as obvious as
> the banding described in the article. As an example, I had a title saved
> as a style in Premiere that I used throughout a project. When I created
> it, I inadvertently stuck a single pixel off to the side -- that's one
> pixel out of a 720 x 480 frame. I had no trouble noticing it.
Sure, on a hard edge you will have no trouble. I had not a whit of trouble
spotting three dead pixels out of 10,200,000 on my Dslr pictures because
they were white. Now that they have been remapped to the values of their
neighbors I don't have a hope in hell of ever spotting them again, no matter
how closely I look.
>
>>
>>
>>
>>>
>>>> For what it's worth, I've only rarely found such a banded frame on any
>>>> DVCAM footage I've shot, which indicates to me that DV is right on the
>>>> edge of reliability. DVCAM, with its 15 micron track width, or DVCPRO
>>>> with its 18 micron track, are sufficiently on the safe side of the
>>>> bleeding edge so that this sort of droput is much less likely to occur.
>>>>
>>>> Bear in mind that analog BetaSP typically has several dropouts per
>>>> minute; the last time I measured visible dropout rates on Hi8 and S-VHS
>>>> I got numbers in the range of a dropout every 3-5 seconds (Hi8) and
>>>> every 7-20 seconds (S-VHS). One visible dropout per hour-long tape, on
>>>> average, is not something to get flustered about. But if it does bother
>>>> you, shoot DVCAM or DVCPRO instead."
>>>>
>>>> "Digital Dropout: DV is highly resistant to dropout because the same
>>>> data is recorded multiple times within the track. The playback
>>>> electronics compare the multiple data streams, and reject those that
>>>> are corrupted by an oxide particle dropping off the tape. The dropouts
>>>> are still there, but you don't see them on the screen. But if the
>>>> dropout is big enough, the correction circuits don't have enough data
>>>> to work with, causing digital dropout, which results in a sudden
>>>> blockiness in the picture. The worse the dropout, the larger the
>>>> blocks, until the picture is lost completely. They are much rarer than
>>>> analog dropouts, but they're much more noticeable when they do happen."
>>
>> Read the last part of this carefully, starting with: "But if the dropout
>> is big enough..."
>>
>> No comment on this, counselor?
>
> Do you see any quantification of this kind of error? I don't.
I've seen them when they are large. I've seen them a number of times on
miniDV. I've never seen one on DVCPro, and I've shot and edited over 3000
hours of material on that format, including numerous documentaries in which
I jog through single frames repeatedly while setting up edit points.
>
>>
>>>>
>>>> Finally, view this pdf file if you want to see dropout rates of DV vs.
>>>> DVcam graphically displayed with counts/min.
>>>>
>>>> http://www.pmdmagnetics.com/displayfile.asp?id=48140.
>>>>
>>>> It's pretty good, but it ain't perfect.
>>>
>>> It's completely irrelevant. The metric is: "mitigated" errors versus
>>> perfectly corrected errors.
>>
>> Banding shows an unrecoverable error. Block replacements signify
>> unrecoverable errors. I've presented you with evidence that such errors
>> do indeed exist, and in fact one source (a professional, no less) has
>> given the approximate rate of such errors on DV tapes, which he compares
>> unfavorably with that of DVCam.
>
> I never said they don't exist -- that's a Martin argument. I said that I
> don't have any reason to believe that they occur so often as to result in
> generational error. As I've said repeatedly, quantify these kind of
> errors. Until you can, you're just speculating, and I have no interest in
> speculation.
This completely depends on what you mean by generational error. I read in
one forum a post in which it was claimed that it takes about 150 generations
in DV before one starts seeing noticeable degradation. This is anecdotal,
but assuming that it is true that is so superior to any analog format that
it might as well mean that there is no generational loss, but in reality
unless you can make infinite copies and the last is as good as the first
then there is generational loss of some kind. If there is a single
unrecoverable error which occurs when copying tapes, then there is
generational loss, by definition. It is certainly "virtually lossless", but
unless you would like to argue against the validity of the second law of
thermodynamics then sorry, there is always loss in any closed system.
>
>>
>> The simple fact is that if DV were really error-free there would be no
>> reason at all to have DVCam and DVCPro formats, and even if those formats
>> existed only for the purposes of marketing, professionals would soon
>> learn that they could save lots of money by using DV instead.
>
> DVCam and DVCPro formats exist because they are more resistent to drop
> out. What has that to do with this discussion?
If dropouts are always recoverable, then there is absolutely no reason to
resist them.
>
>>
>> As a professional in this business for well over twenty years, I can
>> assure you that not a single network or production company with which I
>> have contact here in Japan (CNN, NBC, CBS, ABC, ABC Australia, ORF, ZDF,
>> ARD, BBC, Reuters, APTN, Swiss TV, NHK, TBS, Fuji TV, TV Asahi, NTV,
>> SBS, YTN, MBC, KBS, to name the main ones) uses miniDV as a primary
>> aquisition source or within the production chain post-acquisition. There
>> are reasons for that, and one of them is not that they like to spend more
>> money than necessary.
>
> I'm sure that's true. What has that to do with this discussion?
Dropouts are not always recoverable, so money is spent resisting dropouts
because it is in the economic interests of professionals to not have
material with visible dropouts.
>
>>
>> Now you can huff and you can puff and make a lot of fancy noise and pull
>> your lawyerly rabbits out of your lawyerly hat-- you might even win your
>> case with clever sophisms--but that doesn't change the reality one whit.
>
> Except that you don't know what reality is, despite my asking you to tell
> me. Quantify the "mitigated" error rate. If you can't, you're just
> blowing smoke. That's not a "sophism," but a simple fact. Evidence is
> compelling. Opinion isn't.
Quantify the number of meteoric impacts on North America per year. I'll bet
you can't, but that doesn't mean that there aren't any.
Toby
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