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RE: arsclist ADAT recovery
I have not baked ADAT tapes so I cannot offer any specific comment. I
have baked other tapes - not recently. Here are some of the things I
noted.
I agree with Peter that there is not a single recipe that will work with
all tapes, particularly because different tapes have different problems,
and also consider that the basic design of different tapes can be REALLY
different. Compare for example an ADAT tape with a 2" 24 track mastering
tape. I can't think of much that they really have in common. The
thickness of the base, size of pigments, and binder systems are likely
to be very different. Just think of the thickness of the base alone -
and you don't have to go any further then that. Peter is also correct
that some tapes should never be baked - but these are usually because of
unusual circumstances - such as tapes that are or have been contaminated
for example.
I believe that I may be more cautious then some and here is why. Some
years ago - as in the early 90's I was experimenting with Baking and the
RF output I was getting out of the tapes. Ultimately what really matters
with tape is the RF output - an attenuated RF output will obviously
product a poorer quality playback. There are several reasons why one
could get an attenuated RF output - including the possibility that
baking could somehow effect the orientation or coercivity of particles
(I am not suggesting this - just the point that there are several
factors that should/could be considered). Anyhow... there were several
tapes that I processed that seemed to have attenuated RF output after
baking. The sticky shed was lessened in these tapes, but so was the RF.
I could not figure out why. What I did was take out some magnetic
developer and look at the tracks in certain areas of these tapes. What I
noticed was an increased skew to the tracks. I did not have equipment to
precisely measure the differences, but it was quite apparent on
examination that there was a difference between before and after. It was
also not visible on all sections of the tape. So some sections of the
tape had more and some less, and the skewing would sometimes appear to
be more accentuated in areas across the tape and not in others. This was
true for several tapes. Also - for what it is worth - the Ferrofluid
seemed to illuminate the tracks differently after baking. It still
worked, but the color of the bands were different - and that supports
the theory that there is a chemical reaction that occurs. Same tapes,
same ferrofluid.
So here is my theory - I believe that the PET when heated will partially
try to return to its original orientation and shape as they were
manufactured in Jumbos, before coating and slitting. It is well
documented that many plastics have a "memory" and when heated lightly
will tend to want to go back to an earlier configuration. It appeared to
me that the skew was non - linear, and inconsistent. That would support
(no pun intended) this idea of base film stretch and shrinkage.
Longitudinally recorded media will likely be unaffected by this
deformation because the tracks are relatively wide, and the percent of
stretch or shrinkage is small and therefore not an issue. With helical
recordings, however, it is a totally different matter.
I never went further with the tests, but I believe that this is
something that can be relatively easily done with pre recorded test
strips, carefully measured before baking and after. Several different
temperature and RH conditions may be applied, and it is possible to use
a microscope and measure the tracks and guard bands (I would use a
non-azimuth recording format for the test) and most importantly the
angle of the tracks. I would try this for several tape formulations and
types.
Based on what I found - I believe it is better to be prudent with
valuable recordings. Most facilities do not have adequate
instrumentation to measure RF output. The approach of "well it plays"
does not really cut it. You need to measure RF output before and after
treatment with a carefully calibrated system. This, fortunately, can be
done - as I did some years ago. I believe that some more work needs to
be done in this area before it is fair to say what techniques really do
to the tapes. As Peter mentions there are other techniques like
dehumidification too - but these need to be tested as well. Looks like
the start of a good doctoral dissertation to me!!
James Lindner
Managing Member
Media Matters, LLC.
15 Washington Place, Suite 2M
New York, N.Y. 10003
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-----Original Message-----
From: owner-ARSCLIST@xxxxxxxxxxxxxxxxx
[mailto:owner-ARSCLIST@xxxxxxxxxxxxxxxxx] On Behalf Of list
Sent: Wednesday, November 27, 2002 1:34 PM
To: ARSCLIST@xxxxxxxxxxxxxxxx
Subject: RE: arsclist ADAT recovery
Joav:
ADAT tapes can suffer from both dry shedding and binder hydrolysis
(sticky
shed). Baking, if done correctly, should not result in unrecoverable
tracking errors- it never has at our lab. Of course, just like anything
else, baking must be done properly and not every tape should be baked
the
same way. Temperature levels, duration and ramping sequences must be
applied appropriately for the material being processed.
One of the problems with baking is that it is seen as a
"one-size-fits-all
universal panacea". Baking procedures that stabilize one tape
formulation
may be totally inadequate for others while higher temperatures safely
applied to one type of tape can seriously deform other tapes. Some
tapes
should never be baked. ADATs can be safely baked but I would not
recommend
it in some sort of the makeshift oven. We use laboratory equipment that
is
extremely adjustable and is stable to within 1/2 of a degree. As a rule
of
thumb, ADATs should be processed at a lower temperature and longer
duration
than 2" or 1/4' audio tapes.
If someone is paranoid about the baking process, we also offer a service
that produces similar results using an environmental chamber but the
processing time can be measured in MONTHS.
Peter Brothers
CEO
SPECS BROS., LLC
peter@xxxxxxxxxxxxx
www.specsbros.com
Tape Restoration and Disaster Recovery Since 1983
> -----Original Message-----
> From: owner-ARSCLIST@xxxxxxxxxxxxxxxxx
> [mailto:owner-ARSCLIST@xxxxxxxxxxxxxxxxx]On Behalf Of Richard L. Hess
> Sent: Monday, November 25, 2002 12:43 PM
> To: ARSCLIST@xxxxxxxxxxxxxxxx
> Subject: Re: arsclist ADAT recovery
>
>
> Joav,
>
> If it's any help...
>
> I understand earlier U-Matic (3/4-inch) video tapes suffer from this
and
> other loss-of-oxide decay scenarios.
>
> I've also seen messages from Jim Lindner that say that the dimensional
> shifts introduced by baking may (will?) cause unrecoverable
> tracking errors
> in the higher density video (and presumably) ADAT tapes.
>
> I haven't run across anything more than this. Hopefully Jim and
> others will
> respond.
>
> Cheers,
>
> Richard
>
>
> At 09:17 AM 11/24/2002 +0200, Joav Shdema wrote:
> >I am sure many of you have encountered problems with ADAT tapes over
the
> >years just like we have. Recently I was sent a master recording
> of a French
> >artist of the early '70 which was transferred to ADAT some 12
> years ago (the
> >early blackface recorders). The tape now presents plenty
> dropouts and errors
> >and was sent to us because the record label gave up on it. They are
now
> >looking for some Voodoo miracle to save their case.
> >It occurred tome that ADAT, Super VHS, tapes were made from material
that
> >may have been another victim to the sticky shed problem. This Ampex S
VHS
> >sure looks suspicious.
> >I was wondering if anybody on the list had similar experience
> and what was
> >the remedy?
> >
> >Best,
> >
> >Joav Shdema
> >Producer / Engineer
>
> -
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>
-
For subscription instructions, see the ARSC home page
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Copyright of individual posting is owned by the author of the posting
and
permission to re-transmit or publish a post must be secured
from the author of the post.
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For subscription instructions, see the ARSC home page
http://www.arsc-audio.org/arsclist.html
Copyright of individual posting is owned by the author of the posting and
permission to re-transmit or publish a post must be secured
from the author of the post.