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Re: [ARSCLIST] Re print-thru

Hello, Lou, Will, and Aaron,

I started this this morning and then was going to post it on my blog and now that Goran and David Breneman have posted, I thought I'd send off part of what I wanted to say.

This is a very interesting discussion and I think there are some unknowns here.

First, I agree with Lou that the tension in different modes depends on the machine. The rule that a play wind is better than a fast wind came from the days of Ampex 300s and 350s, I think. As you may recall, these had play and then flat-out fast wind. While the torques were adjustable with those hot slide resistors, these were constant torque machines. More about constant torque later.

As we moved forward (and perhaps backward) we have seen single-motor consumer machines (including the Ampex 600 et al) as well as servo-controlled, constant tension studio machines.

The consumer machines produced horrid fast winds but many tapes would fast-wind well on later professional machines.

A second thing to consider is the slitting of the tape and how air is entrapped between layers in how it winds. Remember the German folks especially used pancakes in radio and did not use reels. U.S.A. tapes did not perform as well in that environment. However, at least one of the things which caused those tapes to have fewer popped strands in addition to the superior slitting -- at least as I understand it -- was that the surfaces were a bit rougher at a microscopic level. However, at least some tape researchers in North America felt that the added roughness, while it contributed to smoother tape packs during high-speed wind due to better air removal, also raised the level of asperity noise. Some might argue that asperity noise is a non-issue with AC bias and erase, some might argue that it still is a factor. I think I come down on the second side of this as the phase of the AC bias can't be linked to the particle size.

One of the challenges in winding tape is that there are conflicting requirements.
--It is good to get a smooth pack.
--It is good not to wear out heads to get the pack.
--It is good NOT to have too much pressure on the outside as
that can lead (especially on 7" and smaller reels) to hub
compression and thence to spoking.

Here are some thoughts I've posted over time to my BLOG concerning winding and tape packs. These are from the oldest to the newest.
Wind tape at low speed (library wind) entirely onto one reel after use.

As you can see over twi years there has been a progression of thinking as I learned more about tape structure.

If we look at print through for a moment--and I had pulled Mallinson "The Foundations of Magnetic Recording Second Edition" to do it right but just don't have the time--, there are two factors which can effect its creation and/or its severity. One is the percentage of magnetic domains that are very sensitive to being magnetized and the other is distance between the two layers of the tape. Heat may play a part in this.

If some magnetic domains are very sensitive to being magnetized, then they can be magnetized by the adjacent layer. This can be made worse -- much worse -- if there is a bias field (perhaps even the earth's magnetic field, but usually larger that causes these domains to be ready to flip.

So these annoying domains have taken a magnetic "print" of the layer below (or above) and have a small shadow of that magnetic signature. Winding through the tape does several things, one is that it sets the tape down against a different part of the reel and perhaps that helps self-erase this faint image as it tries to pick up the "new" image of its new neighbour. Print through does increase over time, and I have heard arguments both ways concerning whether there is a practical limit or not. The more I think about it now, I think there might me as given a particular storage environment (temperature, humidity, and magnetic "bias") at some point all of the weaker domains that are available to flip will, and then there will not be enough energy to flip the stronger domains.

I think we look at the distribution of the "sensitivity" of the domains along a bell curve. There are some that will flip with the slightest trigger and there are some that may not flip. Most will flip in the middle say third.

I think the bell curve is linear but our hearing is logarithmic, so even a very small number of domains at the weak end of the bell curve flip, we'll be sure to hear it if it's not masked by louder noise.

I wish Eric would work on the skimming circuits of his A820. I would be VERY interested in the results of that. Goran, have you ever used skimming? The archive would have to be OK with this. I would suggest doing a transfer with the tape "as is" and getting as good a transfer as possible with the crosstalk, and then try the skimming. The risk is that the tape will be partially erased and that high frequencies MAY be erased more than lower frequencies.

I hope this helps -- I don't have this well enough presented yet for my blog. Someday.



Richard L. Hess email: richard@xxxxxxxxxxxxxxx
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.

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