Hello, Corey, Brian, Tom, and Chris,
I think this is phenomenally interesting and am not surprised.
Chris, I think you are lucky recovering tapes from the 1960s. There was
actually the introduction of a new problem in the 1970s with the change
to polyester polyurethane binders on tapes. This change in binder
material also was accompanied by a change to back-coated tapes where
there were two binders in contact with each other.
So yes, tapes from the 1970s and later are more problematic than simpler
tapes from the 1960s in many instances.
Our good friends in Austria may be close to disclosing a long-term fix
for vinegar syndrome, so that side of early tapes may be covered soon.
Thanks to Nadja Wallaszkovits and others for their work on this.
Back to the specific subject at hand:
While the precise mechanisms have been discussed at length, I am not
aware of a completely definitive molecular-level model of this process
(degradation + baking) that is fully accurate and complete. This is
discussed obliquely in my ARSC paper of a few years ago.
I am not certain how the time and temperature curves interact, but,
obviously there is a certain amount of energy under the curve as long as
one stays away from trigger points. I recently researched PET film a bit
more and found that the glass transition temperature (Tg) of the
basefilm is considered to be about 70 °C while its melting point is
around 250 °C.
Let's look at the temperatures involved:
The Ampex patent uses both 50 °C and 54 °C. Corey's post indicated that
they used 48 °C.
There is not a huge difference between 48 °C and even 54 °C when the
next step of possible risk is 70 °C. (Sorry, science is done in °C, but
these four temperatures are 118, 122, 129, and 158 °F.) However, I am
not generally comfortable exceeding 54 °C.
The usual concern for digital audio tape is that the dimensional
stability of the basefilm will be damaged. If the Tg of the basefilm is
70 °C, then I don't think we need to worry at 54 °C or below, especially
with a melting point of 250 °C or so.
The Tg of the mag coat of one squealing tape, by the way, was measured
at about 8 °C. This helps support my cold playback concept. (Tg is the
point where the surface changes from glass-like to rubbery).
There is another thought process involving long-term degradation as
plotted against time as well as the amount of treatment needed to make
the tape playable.
If we look at some critical times we can see perhaps:
Onset of SSS
Almost impossible SSS
Within a short period (less than a year?) a tape goes from playable to
needing baking. This appears to be anywhere from 5-10 years from date of
Of course, all of these timings are modulated by storage humidity (and
to a lesser degree temperature and the fluctuation of both).
At some point, casual baking (4 hours or so) stops being effective.
Let's say that's Medium SSS.
Further on, we find we need to bake for 24 hours or a bit more. Let's
say that's Heavy SSS.
At some point we see Almost Impossible SSS with one reel I was
successful with taking four 48 hour cycles to make it playable (it was
not playable after two, and thinking this is all logarithmic, I just
doubled the previous baking).
So, with these digi tapes we are in the early stages and they are
responding just like analogue tapes did back in the 1980s and 1990s. One
factor that is making the digi tapes easier to bake is that the coatings
on the digi tapes are thinner than on the analogue tapes.
I predict that digi tapes will require longer baking times down the
road. Corollary to this thought: TRANSFER ALL THE DIGI TAPES NOW before
they become a bigger problem (not to mention machine parts availability
which is far, far worse now than analogue) and the parts are finer, less
generic, and more complex...is there a warning in that?
What is Ampex 467? I have no idea what Ampex 467 really is other than a
cool-looking marketing number that combines the 400 designation of the
successful Ampex analogue line (406, 456, 407, 457) with the sleek "jet
age" favourite digit of Boeing (707, 727, 737, 747, 757, 767, 777) and
an arbitrary tens digit that is greater than 50.
The reason I am so cynical about this is that 467 was used on DASH and
(R)DAT tape and I am pretty certain the cross-section of these tapes is
not the same. I have 1/4-inch 467 here (and it did not seem to suffer
from SSS in 2006 or so when I played with it for the paper) and I don't
think it looks/feels like anything a DAT machine would be happy playing
(if slit to the proper width). While thin, it is not DAT thin.
I have had one happy experience baking a DAT tape within the last six
months (and no unhappy experiences ever...unhappy is defined as making
the tape worse). Here is a sample of one that DAT baking is also a
possible contender to solve that format's problems.
One possible "end game" scenario for all this is someday baking a tape
for a week or two at 54 °C and finding it still doesn't play. Did I
mention do it now? I'm glad to hear all the DASH copy work is going on
as I know that was a heavily relied upon format in Hollywood.
Corey and Brian, please send me a private email
([log in to unmask]) giving me permission to quote your posts on my
Degrading Tapes page. I think this is hugely important information as I
have been asked this question recently by someone who is running into
the same problems.
On 2012-02-03 10:57 AM, Brian Bartelt wrote:
> My company, Post Haste Sound, was tasked by MGM to help migrate their DASH library. We found that many many elements were exceptionally problematic despite their relatively young age.
> We experimented with many different ways to improve playback and found low temperature baking to be the most effective method to improve playback, and ultimately had a playback success rate on the project of over 97%.
> Using these techniques we are now beginning other similar DASH migrations for other clients, as people continue to discover that their DASH assets aren't aging well.
> On Feb 2, 2012, at 11:34 PM, "Corey Bailey"<[log in to unmask]> wrote:
>> Hi All,
>> I thought the members of this list might find this interesting:
>> Recently, some 1/2-inch Sony DASH (3324) format tapes were shipped from
>> the UK to the Warner Bros. Sound Transfer Dept in Burbank, CA. The tapes
>> would not play and exhibited Sticky-Shed Syndrome.
>> I was asked if I thought it would be safe to bake the tapes. My response
>> was that it could be risky and if we were to attempt it, the tapes should
>> be baked at a much lower temperature for 24 hours or so. It was decided to
>> try my suggestion since there was nothing to loose at this point.
>> The details:
>> 3 reels of Quantegy 1/2-inch 467 Digital audio tape, originally recorded
>> in August of 1999.
>> 2 reels of Quantegy 1/2-inch 467 Digital audio tape, originally recorded
>> in May of 2004.
>> The tapes were baked for 16 hours at 118 degrees F. and then left in the
>> oven for 6 additional hours as the oven cooled. The decision was made to
>> end the baking at 16 hours because the Transfer Dept. Supervisor wanted to
>> test the results to see if there was any improvement that might warrant
>> further baking. The first tape tested played just fine so each tape was
>> tried in succession with the same positive results.
>> Corey Bailey Audio Engineering
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Quality tape transfers -- even from hard-to-play tapes.