Thank you for posting that detail.
As you are aware, the stick-slip that causes this is related to the
resonance frequency of an unsupported length of tape and its elasticity.
You are probably closer to people who really understand this than I am.
I am wondering how narrow your spectrum analysis was in this, because
you say pairs of 8/9, 16/18, and then 26/28 when I would expect 24/27
(third harmonic of 8/9). The reason that I'm saying this is in my
experience in trying to remove these signals they tend to be clustered
around a given frequency based on the dynamic properties of the
stick-slip process and the mechanical resonance of the unsupported
length of tape, but they are not clean tones as Gregorio is describing.
They generally cannot be "notched" out by a Q > 10 notch filter.
The other thing I am wondering about is when you say:
> The other effect were heavy oxide losses after treatment.
It would be great if you could explain that in more detail. As I
understand what you have written, there were different baking times and
at some point the squeal stopped, but there were still heavy oxide
losses. Did these losses increase with baking time? If so, that is a
very bad indicator.
I had never thought that baking was a good choice for the problematic
I do not know what position you will be in to do further tests, but I'm
wondering if you could attempt to measure the glass transition
temperature (Tg) of the magnetic coating of these tapes. I am wondering
if playing the tapes back in the cold would stop the squealing. I have
tried that on some 3M tapes and the major player in the
not-repaired-by-baking squeal, Sony PR-150.
The concept here is that, at room temperature, the mag coat surface is
no longer glass-like, but rubbery as the Tg of the mag coat as fallen as
the coating degrades. One mag coat that Ric Bradshaw measured for me
while he was still at IBM was 8 °C. So, playing back below the current
Tg works as the tape is not rubbery. We have had fair, but not perfect
success reported with this technique, but it is another worthwhile tool
in our toolbox.
Is any of the BASF shedding sticky/gummy or just powdery?
On 2012-02-06 5:55 PM, Katrin Abromeit wrote:
> Dear Gregorio and all,
> for my bachelor’s thesis, that I wrote within the framework of ILKAR
> (Integrated solutions or Preservation, Archiving and Conservation of
> Endangered Magnetic Tapes and Cylinders) at the Rathgen Research Laboratory
> Berlin, I started to research the effects of heat treatment (baking) on
> sticky tapes made of Polyesterurethane. I digitized my samples (back coated,
> no given brand type or manufacturer) prior and after baking.
> The audible squeal (first intermittedly, later persistently consistent, like
> Joe describes it) manifested itself in the digifile as distortion with pairs
> of peaking frequencies at eight and nine KHz, louder parts would show
> distinct overtones at 16 and 18, as well as 26 and 28 KHz. So, in the file
> the continuous squeal became a content-dependent distortion.
> After baking (54°C, 15% rH,different treatment times), that distortion /
> those peaks disappeared, so they were stickyness-related. The other effect
> were heavy oxide losses after treatment.
> The work is planned to be published in the near future, after it is graded.
> Katrin Abromeit
> Student of Conservation / Restoration of Audiovisual and Photographic Heritage
> University of Applied Sciences, Berlin
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.