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Hi Richard

By what mechanism does "winding the tape back and forth a few times" work?  Is it due to a magneto-strictive effect (which is exaggerated by B-wind) or is it from winding the tape across mildly-magnetised materials in the tape-path (somewhat akin to skimming)?    

It would be interesting make comparisons using the head-bypass feature of a Studer A810.

Best wishes
Nigel

-----Original Message-----
From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Richard L. Hess
Sent: Thursday, 24 October 2013 10:48 a.m.
To: [log in to unmask]
Subject: Re: [ARSCLIST] Advice needed on removing / minimizing tape bleed-through

Hello, Josh,

You are working with what is called "print through" and has been the scourge of tape recording from the beginning.

Technically, there are magnetic domains that are easily flipped. The magnetism from the adjoining layer and perhaps a bias field (including the earth's magnetism) might have encouraged these easily-flipped domains to line up with the magnetic field from the underlying or overlying layers of tape. In either case, the field has to go through one layer of tape to cause this to happen.

Some very loud "bangs" have been known to print through several layers of tape on the reel.

Storing tape tails out tends to bias the print-through process to be post-echo more than pre-echo, or so the theory goes and winding tapes back and forth a few times may also assist in reducing the print through.

Some have suggested winding the tape in B-wind (oxide out) and leaving it for a while, I have not tried this.

Not for the faint of heart, some success has been reported using permanent magnet partial erasure OF THE TAPE by a device you place against that tape as you wind it. This was made in the 50s or 60s by a tape manufacturer and I believe it came in two strengths. There was an Audio Engineering Society paper or preprint on it that I recall seeing years ago. You may search at aes.org in the library. "print through" is a good keyword, I would think.

Finally, some versions of the Studer A820 incorporated controlled erasure called "skimming". I have never used it, but it works on the same principal, but uses the AC bias (high frequency) signal to do the partial erasure.

So we're looking at randomly orienting the particles that were easily reoriented in storage to mirror the adjacent layers of tape.

Obviously, any of the intentional partial-erasure techniques, if over-applied, could have devastating effects to the recording.

Good luck with this.

Cheers,

Richard