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

[Jim Wheeler <Jimwheeler@aol.com>]

Backcoated tapes produce smooth packs at high speeds.  A smooth pack
is critical for archival tape because popped strands are susceptable
to damage. Also, many tape recorders have been designed with fast
starts and stops in high speed shuttle.  Without the backcoat, the
tape pack will slip.  Slippage will cause creasing and foldover
resulting in cracked oxide.

The carbon in the backcoat eliminates electro-static discharges
during high shuttle speeds.

The only "problem" I have seen with backcoat is the sticky-shed gunk
oozing onto the surface but it would also do that on non-backcoated
tapes.

Thicker tape will reduce print-through and that is important for
audio master tapes.  1.5 mil tapes will not have poor head-to-tape
contact IF only 1.5 mil tape is used on the machine.  Tape thickness
changes the head contour so optimum output will be obtained if you
never switch between tapes of different thickness' on a given
machine.

I would never recommend using pancakes except in a bulk duplicating
operation. I ran a lot of tests at Ampex with different flanges.  I
discovered that flanges require windows to allow the air to leak out
as the outer layer is being packed onto the takeup reel in high
speed shuttle.  A very small window (like some old Memorex tapes)
does not allow air to leak out fast enough.

The name-brand tape manufacturers do market tapes with a stable
binder.  You can contact the tape manufacturer representatives and
ask which tape they recommend.  They have a legal problem because
they cannot admit that some tapes are made with a binder that will
breakdown in a moist environment.

Videotapes require some abrasivity to maintain good head-to-tape
contact. The amount of abrasivity varies with each tape
manufacturer.  The shape of the RF envelope tells the story.  If the
envelope is square, the head-tape contact is intimate and is wearing
the video heads.  The ideal RF envelope is one that is slightly
rounded at the start and the end since that indicates that there is
some air film between the heads and tape.

Relative humidity changes the head-tape contact.  Below about 40
percent RH, the video heads do not contact the tape.  Around 60
percent RH (and higher), there is no spacing between the video heads
and tape.  This is a great way to play a tape with poor output but
it will wear the video heads.

Jim Wheeler