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Posted by PTravel on 07/14/06 00:29
"Toby" <kymarto123@ybb.ne.jpp> wrote in message
news:44b6e10a$0$74478$bb4e3ad8@newscene.com...
>
> "PTravel" <ptravel@ruyitang.com> wrote in message
> news:4hnbilFdriuU1@individual.net...
>>
>> "Toby" <kymarto123@ybb.ne.jpp> wrote in message
>> news:44b5b15e$0$65941$bb4e3ad8@newscene.com...
>>>
>>> "PTravel" <ptravel@ruyitang.com> wrote in message
>>> news:4hfsbtF1rcvsvU1@individual.net...
>>>>
>>>> "Richard Crowley" <richard.7.crowley@intel.com> wrote in message
>>>> news:e8ucis$8o5$1@news01.intel.com...
>>>>> "PTravel" wrote ...
>>>>>> We're still talking about apples and oranges -- data reconstructed
>>>>>> using ECC is accurate and bit-for-bit what was recorded (or supposed
>>>>>> to have been recorded).
>>>>>
>>>>> No. That is the description of how ECC works for computer
>>>>> data. There is another MAJOR error recovery layer used by
>>>>> audio CDs, DVDs, DVD tape, etc. It is how they manage to
>>>>> be cost effective.
>>>>>
>>>>> Audio/video data that cannot be accurately *corrected* gets
>>>>> *mitigated* by extrapolation. This is the factor that is present
>>>>> in audio and video digital recording but NOT in computer data
>>>>> recording. It probably comes into play more often than we think,
>>>>> but if it is good enough we don't notice. But multiple repetitions
>>>>> of it amount to something approaching "generation loss".
>>>>
>>>> Can you site me to something that says how often this happens? I've
>>>> never heard of DV video transfers being described as anything other
>>>> than lossless.
>>>>
>>>>>
>>>>>> Replacing pixels (or scan lines or averaging blocks) results in lost
>>>>>> data.
>>>>>
>>>>> I think you have that backwards. Replacing pixels, etc. is one
>>>>> of the major migitating actions taken as a result of lost data.
>>>>
>>>> I meant that the resulting data is not the same as the original, hence
>>>> there is data lost. But how often does this happen?
>>>
>>> This reminds me of a story. How often do you think earthquakes happen in
>>> Japan? Once a month? Once a week? We recently did a doco about
>>> earthquakes here and visited one of their seismo centers. It turns out
>>> that the rate of measurable earthquakes is about 100 an hour.
>>>
>>> Do you see what I am getting at?
>>
>> Yes, which is exactly what I've been getting at. Borrowing Martin's
>> terminology, what is the ratio of mitigated errors to fully-corrected
>> errors? If it's comparable to the ratio of major earthquakes in Japan
>> versus small tremors that no one notices, then we're looking at Richard's
>> guestimate that works out to 1 mitigated error per 666 hours of video.
>> With that kind of rate, miniDV is, for all intents and purposes,
>> lossless.
>>
>> However, we remain in the realm of speculation -- without hard data, this
>> is all pointless, and I'll stand by my position, i.e. there is no
>> generation loss for D-25 transfers.
>
> OK, here are a couple of clues. First a quote from an ad for Sony tape:
>
>
> "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).
>
> 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.
Hard evidence. Not speculation.
>
> 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?
> 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.
> 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.
> 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."
>
> 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.
>
> Toby
>
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