Hi guys - Used to work for Memorex as a QA Engineering tech years ago - I haven't heard of the term "looping back" but it sounds like the type of transport problems you can get if tape is either too well polished, backing (mylar)too limp, or both. What happens is that the tape is too conformant to surfaces of the machine (heads, guides, sometimes pinch rollers) so the tape sticks to the guide or pinch roller on its way thru the tape path. This will cause the tape to wind around the pinch roller and ball up -
The other possibility that could be meant by that phrase is that higher output tapes have more of a tendency to "print through" - This is where the "oversexed" magnetic domains on one layer of tape, when left in contact with the next and previous layers, will "print thru" the backing and cause an echo on the next layer. If the recorded tape is stored with the same "wind" as it comes in the box, when it is played back you will hear "pre" echoes. Neat effect if you want it, really bad if you don't. Consequently, virtually all analog tapes are stored "tails out" after recording - this doesn't eliminate the "echo", it just becomes a "post" echo, and sounds more intentional.
"In other words, if you've run 456 on your machine for a long time, than there will be worn patterns in the parts of your machine that the tape runs across. The change to GP9 is not going to react well to those pre-worn patterns. I don't know what do you think?"
I think the Quantegy tech tried to snow you or else didn't know the real reason. Any time you run ANY tape over the guides and heads of a tape machine, you are constantly polishing the surfaces which contact the tape. Mag tape is made in typically 24" to 36" width, then slit down to the final width in stages, and normally doesn't have any noticeable side-to-side differences in stiffness or oxide coating - therefore, if the machine is properly aligned physically, there should be even wear patterns across the width of the heads and guides. As far as wear vs. type of tape, there should be no difference in how a given type of tape tracks through the machine. However, getting back to properties of surface roughness and backing stiffness, these can and will change the coefficient of friction between the guides/heads and the tape. This can cause tension variations along the tape path, stuttering of the tape speed due to stiction (not a made-up word, wet the tip of your middle finger slightly and run it along a smooth countertop at a steep angle, so that it "chatters" along - this is similar to what happens with a highly polished (well-used) tape path and highly polished tape. If you have a copy of Boston's second album (I think that's the one) There's a horror story about their master (and only) 2" tape and too much polishing of tape and machine (100's of passes on same tape) - this is a really severe case of stiction.
If the term means something entirely different, maybe someone who's heard of the term will chip in... Steve
