[no subject]

In some respects DTV proves the point quite nicely in that materials
with reduced bandwidth and resolution will clearly look worse when
encoded (and particularly upconverted) then materials of full bandwidth
and full resolution.  Better looking material will have more utility in
production and therefore be more valuable.  I think that this means that
you do not intentionally reduce bandwidth if there is no reason to do
so.  If you already have high bandwidth should you reduce it for
archival storage?  I think that the answer is clearly no.  Materials
that have been acquired in already reduced bandwidth is another issue -
if you have already lost it.... there is no going back.

When we get out of the strict "video" world of compression and discuss
more "net" compression - things get much much worse very quickly.
Consider - A job edited on an avid with proprietary mjpeg is then made
into - a REAL video stream - A MPEG 2 DVD - and a Sorenson streaming
version.  Consider the job in parallel and it is currently a nightmare -
consider the problem in a serial problem and it is your worst
nightmare.... and that is the rub for an archive - you cannot guarantee
how the materials will be used in the future - so for the archive it is
getting much, much more complicated and video compression issues like
discussing DigiBeta versus DVCPRO50 are nothing when discussing all of
the issues in the various streaming software options and technologies.

Compression is a fact of life - it always has been... but for an archive
the job of preserving the material for the future becomes the serious
business - and to some extent protecting the material from loss due to
many perils is an extremely important part of the job.  Degeneration or
loss from many things - from fire and flood - from over eager "spring
cleaning", from patron loss, from rerecording over tapes to save money
in the lean years - and yes - including degeneration through compression
depletion - meaning... after you have compressed the compression of the
compression of the compression that was decompressed and then unencoded
and then recompressed before upconverting...... what did the original
really look like in the first place??
No one will know.... forever - and forever is a LONG time.

jim

Jim Lindner - President
VidiPax - The Magnetic Media and Information Migration Full Services
Company
Telephone 212-563-1999
www.vidipax.com
Moderator of A/V Media Matters@topica.com

tvmark@gateway.net wrote:
>Why is D-1 the format for purists but not D-5?  Both are uncompressed,
>and D-5 offers the greater data rate.  Furthermore, its use in HDTV
>makes it the more current format.
>
>As for the rest of the discussion, I would agree that compression is not
>necessarily evil and has many places.  I often use Digital Betacam and
>DVCPRO and have used DCT and Digital-S (to mention some "gentle"
>compression video formats) and often use Musicam and MPEG Layer 3 (to
>mention some audio compression formats).
>
>I DO, however, have two cautions:
>
>1.  Current presentation technology might not indicate problems.  Sony,
>for example, has a demo tape of material shot on HDCAM (4.4:1
>compression of reduced-bandwidth high-definition television).  Some of
>the material was shot with high-definition lenses; some with standard
>lenses.  Shown on Sony's best high-definition direct-view monitor, the
>SD-lens material looks close to the HD-lens material.  Seen on the large
>projection screen at the Sony Pictures Studios High Definition Center,
>however, the SD-lens material sticks out like a sore thumb.
>On the same large screen (fed from an HDIH-3000 projector with
>Nikon optics), I could detect differences between the HDD-1000
>(uncompressed, open-reel), HDCAM, and the HD D-5 (4:1 compression,
>full-bandwidth input to the compressor).
>
>   2.  A single round-trip through a compression system does not indicate
>problems that may be introduced by concatenated compression.  When we do
>a single round-trip through a Layer 3 audio system (128 kbps), for
>example, we cannot detect problems with certain source material that we
>use.  TWO round trips, however (with the particular compression
>parameters in that particular equipment), introduced an audible
>"scratchiness" on certain low-level, low-frequency material.  Newer
>software has eliminated that particular problem.
>   If the sole function of an archive is to provide reproduction on
>site, then the concatenated-compression issue need not be considered.
>If, however, reproduced material may be subject to additional stages of
>transmission or recording compression, then it should be considered.
>     Some processes are being developed to help mitigate the
>concatenation problem.  Part of the debate over the inclusion of
>720-pixel active lines in the U.S. ATSC DTV standard A/53 (instead of
>the current 704) relates to just that issue.  Macroblock misalignment
>between 704 and 720 prevents simple transcoding between generations.
>
>TTFN,
>Mark Schubin
>Technological Consultant

From: Matthew_Davies@screensound.gov.au
Date: Fri, 3 Dec 1999 08:02:43 -0800
To: AV-Media-Matters@topica.com
Subject: [AV Media Matters] A caution / correction re head cleaning
Message-ID: <0.10003996.1988597638-212058698-944236957@topica.com>
MIME-Version: 1.0
Content-Type: text/plain

Moderators Comments:
Isopropyl alcohol as is sold in many pharmacies is not pure. Although I have
not pursued it - I believe that mineral oil is an additive.  I strongly
recommend that you use laboratory grade Iso - sometimes you can get it in
pharmacies sold as 99% Isopropyl at a higher price then the 70% usual stuff
that they sell.  I have not purchased it from a pharmacy in a long time -
but when we stopped it was getting hard to find he 99% Iso - we only found
the cheaper grade which was not even being marked with the purity any
longer - this may just be the NY market however. We buy 99% lab grade in 55
gallon drums - and we can be sure of its purity that way - and of course it
is MUCH cheaper on a gallon by gallon basis.  We decant when we need it with
a special drum pump which we put into squeeze bottles that is specifically
made for lab use - and every now and then we trash the bottles when they get
worn.  Iso 99 also lasts a LONG time if you buy that much of it, but you are
sure that it is not contaminated or diluted.

Also - some materials react very negatively and should not be cleaned with
Isopropyl - such as rubber pinch rollers. The alcohol will dry out the
rubber and ruin the roller. It can do some nasty things to other parts also,
and can remove all sorts of nice decals from old machines.  Actually we use
many different solvents around here - we find that some will do a better job
with some tape debris then others - it all depends on the type of debris -
and then sometimes we need a solvent to clean up the residue of another
solvent (no kidding).  The solvents range in strength - Xylene is one of the
tougher ones - and even acetone is used sometimes for really tough spots -
we still keep a stash of TriClor that is solvent grade and there is also a
pretty wide range of degreasers that we have used also.  We have not found
one that solves all the problems - but Iso is the one used most often, and
if that does not work we get out the other stuff.  Make sure that you have
the MSDS and follow the rules - some of these chemicals are nasty in closed
environments - we usually open the windows wide in a separate area and run a
fan or two - operators with gloves, masks and goggles for the heavy duty
work.

jim

A kind reader has pointed out that methylated spirit is not recommended by
tape machine manufacturers for head cleaning and can leave deposits on tape
heads. Iso-propyl alcohol is available at many Pharmacies  in Australia,
and is much safer due to it's purity. General household grade methylated
spirits is mostly ethyl -alcohol but the additives and impurities are not
completely defined, but may include greases and oils which can be left
smeared on the head, and are quite difficult to remove. When using any head
cleaning solvent, I suggest applying a small quantity with a cotton bud and
then vigorously wiping with a dry cotton bud, this seems to avoid most
problems.

A few principles of cleaning disc pressings :-

Distilled or reverse osmosis filtered water is preferred to prevent
contamination. A surfactant is required to ensure penetration of the water
into the groove, 1% cetrimide solution (ceterimide is also available at
many pharmacies in Aus) recommended. A fine soft brush can assist in
working the slightly foaming water into the groove, and working the dirt
out (ideally use an ultrasonic bath). The next requirement is some method
for removing the last of the dirt and solutions from the disc. Rinsing with
plenty of distilled water works, or if your lucky you can use a Keith Monks
vacuum cleaning machine. Air drying is the final stage, obviously in a
clean environment. Cleaning discs without special equipment takes care and
some practice, but you can achieve good results.