Posted by Steve King on 07/13/06 03:34

"Toby" <kymarto123@ybb.ne.jpp> wrote in message
news:44b5b071$0$65891$bb4e3ad8@newscene.com...
>
> "Steve King" <steveSPAMBLOCK@stevekingSPAMBLOCK.net> wrote in message
> news:LZidncnSMNJykCnZnZ2dnUVZ_uydnZ2d@comcast.com...
>> "Richard Crowley" <richard.7.crowley@intel.com> wrote in message
>> news:e90q9f$hc3$1@news01.intel.com...
>>> "Steve King" wrote ...
>>>> Your comments about the DV standard allowing for bit-errors is over my
>>>> head. Do all DV tapes have bit errors?
>>>
>>> Average 100 per minute according to Sony. They rate
>>> DVCAM at only 50 per minute. But almost all are corrected
>>> by the ECC.
>>>
>>>> If so, and if they accumulate with each transfer, then I guess that
>>>> would be generational loss.
>>>
>>> The ones that can't be bit-perfect corrected by the ECC will
>>> accumulate. To my way of thinking it is the digital equivalent
>>> of "generation loss". I never go past the 2nd generation "digital
>>> clone" of a DV or DVCAM tape, so I anticipate that the error
>>> rate is unlikely to ever affect my day-to-day activities.
>>>
>>>> Oh, and is computer tape as used in backing up the most valuable data
>>>> on the planet different from DV tape? Or, are we really interested any
>>>> more? ;-)
>>>
>>> The physical tape may be exactly the same. But, how the data is
>>> handled on the tape (and how much raw capacity is devoted to
>>> ECC) is different depending on the application (hard data vs.
>>> audio/video data).
>>>
>>> There are many different error detection and correction schemes
>>> out there.
>>> http://en.wikipedia.org/wiki/Category:Error_detection_and_correction
>>> But as with anything, they come at the cost of taking up space that
>>> you could have used for storing data. Media used for computer data
>>> ("Orange Book" CD-ROM, hard drives, computer data backup tape
>>> formats, etc.) expend a significant portion of their capacity on the
>>> pure
>>> overhead of storing checksums, redundant information, etc. so that you
>>> are ensured of a "bit-perfect" data storage and retrieval experience. Of
>>> course, nothing on this earth is "perfect", but computer data medium
>>> are rated at a failure rate so tiny that you may see one only a few
>>> times
>>> during your lifetime.
>>>
>>> OTOH, some digital media which are intended for "soft data" like audio
>>> or video can get away with a higher failure rate because it is both
>>> easier
>>> to extrapolate missing data, AND it is within the acceptable range of
>>> impact to the user to extrapolate rather than guarantee bit-perfect. By
>>> taking up less space for the ECC overhead, they can use more of the
>>> raw capacity of the medium for storing the audio/video data.
>>>
>>> Note that there are some schemes for backing up your hard drive
>>> data to mini-DV tapes, etc. But they add extra ECC overhead to
>>> the data stream before it ever reaches the DV tape, The extra ECC
>>> makes up for the not-quite-bit-perfect performance of DV tape.
>>
>> Thanks for the explanation. Very interesting. Thinking MiniDV
>> generations in our own operation --- our worst case is acquisition
>> tape-HDD-Master Archive DV Tape-HDD-NEW (Modified normally) Master
>> Archive DV Tape. What's that? Four generations from original? That
>> would only happen if the HDD went belly up, since we budget for dedicated
>> drives for many projects or maintain single-client assigned HDDs for
>> multiple projects. We've been lucky so far. It's a joy to be able to
>> use footage in new projects or accomplish client change requests
>> conveniently by simply plugging in an HDD and immediately proceeding to
>> productive work.
>
> My network is starting to archive all material on HDDs. The threshold had
> been reached where it is significantly cheaper to save an hour's worth of
> video on a hard disk than on tape.
>
> Toby

We're too small to arrive at the decision based on experiential data, but
for us the low cost of HDD and the convenience factor is too appealing to
not go that way.

Steve King

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