Re: [AV Media Matters] Re-Evaluating Tape Mastering Stock

[rohre@ARLUT.UTEXAS.EDU]

Greetings to Jim and the group.

Well, I must weigh in as a user of multitrack reel to reel instrumentation
tapes, and all sizes of cassette/cartridge formats.

On backcoating, we have seen Zero failures in over 25 years.  As
I understand it, backcoating should reduce print through as it
provides some spacing between the layers of two winds of tape. We
have never had a print through problem with back coated tapes.  We
DEFINITELY saw an improvement in winding and tape pack, when our
data tapes are cycled frequently over certain sections.

Backcoating came along, and we saw a near elimination of blockshift.
Now, granted, we also undertook a rigorous tape drive maintenance
program and corrected tape path mechanical problems before they
could contribute to tape wandering at that same time, but it seemed
that backcoated tapes always rewound better for us than non back
coated.  Eventually, all our stock was back coated.  Our sponsors
and 3 other data playback labs in our programs using copies we made
on backcoated stock, have never experienced any failures or problems
attributed to backcoat.

 Backcoated tapes were the choice for Masters and long duration
unattended recordings.  I believe the JPL Galileo recorder uses
backcoated 79L or 799 Ampex tape.  It is still functioning.  They
did have a head stiction problem which was in a batch of tape which
I also had, but this seemed to be a sticky shed situation, and was
overcome by jogging the recorder when starting, ie doing a forward
and reverse to "unpark" the tape from heads.

To clarify here, I consider that sticky shed is a different
artifact, and we see it only on the OXIDE side of tapes.  And only
on some tapes. Tapes with older formulations do not have it, and
most recent tapes have not developed it with decent storage.

We also had better experience after back coating came along in fewer
tape layers self tightening on a reel.  That is, they did not cinch
up if back coated, where that had been seen on non back coated
media. Again, our use is instrumentation formulas, and Jim Wheeler
or someone would have to comment on whether they are different from
audio backcoatings.

I have been very satisfied with the Quantegy extensions to the Ampex
line of tapes. We used both Ampex, and 3M Government Services
contract tapes while 3M was still in the instrumentation tape
business.  We briefly tested, in the late 80's, the revived Memorex
line that was made in Italy, but found it unsuited for critical
instrumentation use.  (Note that that reel to reel product was a
different company from consumer Memorex.)

My only experience with BASF abrasivity in recent times was around
early 90's when we worked with Racal of England on developing the
Storeplex SVHS based recorder.  They reported that the BASF video
formulation was very abrasive, and I tested some locally.  It
appeared to develop dropouts in a few plays. Racal even used NEW
BASF as an abrasive head cleaner on the Storeplex prototype we were
testing!  I have used BASF audio reel to reel test tapes in 1996--.
They are of course played fewer times than a working copy, and I
have not seen any abrasive issues yet.

In working with instrumentation formulations over the years, I know
that the chemistry is critical to long life, and there was a
struggle when natural whale oil lubricant was replaced by
synthetics.  The tape making process is a fascinating batch process,
and much can go wrong since a large web of tape is being made all at
one time.  Besides coating problems, which seem to be fewer with
modern controls of the batch line, a critical step is the slitting.
Slitters eventually get dull, and can ruin a batch of tape.  Once I
have seen an end to end inclusion or microscopic surface
imperfection ruin several new reels of 10,000 foot tape.  But, over
the years I have seen several slitting problems in new tape.  It
became a thing of certifying tape, and being able to notify the
factory when slitter blades needed changing.  But, we had excellent
cooperation from the lab and factory on critical programs using tape
in unattended recording, where you could not change the Master after
the mission started, and needed near zero dropouts and uniform track
to track performance. Backcoated tapes also seemed to have less to
no debris left on the heads than other types.

Months of data was successfully recorded each year, all unattended.
The longest recording session was 12 months of recording near the
North Pole at an ice camp.  Of course, this was on-off cycling, a
data logging type of operation.  But, the satellite grade back
coated tape worked flawlessly in a battery powered reel to reel,
seismic recorder.  Back coating also lessens static charge buildup
in tape, and this Arctic tape still retained some static charge a
week after removal from the ice and transport to my lab in Texas!  I
am not sure a non back coated tape would have performed, since it
would have had more static charging problems.  This was the Ampex
79L tape, and we have been a big fan of it, 799, and 797 grades over
its production lifetime.  They were the smoothest, and less abrasive
tapes of several instrumentation grades we used or tested.

With smooth tape, you also have the issue of brown stain in dry cool
climates. This is a microscopic deposit that may form on heads,
reducing signal level by spacing loss according to the Wallace
equation.  The only times we have seen it in our generally moderate
humidity climate here, is in Winter, (always the month of January,
our usual coldest and driest time).  Yet, with mild head lapping, it
can be overcome easily.

Sites like Denver, CO had an annual winter problem with brown stain,
because of low humidity, even in lab environments.  Desert areas
that have 20% or less humidity are subject to it.  Desert rocket
test ranges have a problem even controlling humidity in labs, and
are the usual victims.

With any tape, you have to clean the tape path, and monitor the
environment to obtain optimum results.  With some attention to
detail, tape remains a robust archival form.

---Stuart Rohre
Univ. of TX, Applied Reserach Labs,
Recording and A/D Facility