Ok, this is what I meant when I was questioning whether a de-echo plug-in would work:
"The delay between original and print changes as tape pack diameter changes. "
John said it better than I.
De-echo software that can "chase" echo of varying delay times would have to be quite sophisticated,
unless it's just an automated noise gate (ie it looks for spikes below a certain level and kills
them). Again, I haven't tried this software and I'm not a code-writer, so I have no idea if it would
do the job on print-through.
Richard Hess asked for a sample of bad print-through. I don't have any on my hard drive and don't
have time to hunt for and transfer a bad-example tape. Anyone who has old 2-track duped tapes on
1-mil stock probably has a candidate for experimentation. Richard, what about your old RCA 2-track
tape, or that Mercury 2-track I gave you a few years back? I'm sorry but I don't have studio time
for experimentation right now, maybe a little bit of time next month. Another good candidate would
be any 1/4-track early 60's acetate 1-mil duped tape in your shelves. The smaller tracks and usual
lower level may or may not make the print-through a worse problem (maybe less dynamic range between
original signal and echo, but also maybe lower level echo of lower-level signal, I'm no expert).
-- Tom Fine
----- Original Message -----
From: "John Chester" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, October 25, 2013 12:40 AM
Subject: Re: [ARSCLIST] Advice needed on removing / minimizing tape bleed-through
> At 10:51 PM 10/24/2013, Malcolm Rockwell wrote:
>>There may not be a major problem here. What has printed through is the audio from the next layer
>>of tape, correct? With digital manipulation being what it is today it should be simple enough to
>>grab the full volume layer of audio, attenuate it, flip the waveform and apply it "over" the
>>printed through signal. There will probably be artifacts but if you fiddle with various parameters
>>for a while, such as EQ, you will probably be able to find an acceptable solution to your problem.
>>I'd apply this to softer passages and leave louder material well enough alone, though.
>>It's worth a try.
> There are a number of problems to consider.
> First, the printed recording is not the same length as the original. The delay between original
> and print changes as tape pack diameter changes. Seems to me that for a tape which has been
> stored tails out, the print is longer than the original. (Delay from original to print increases
> as tape pack diameter on the take up reel increases.) The original recording can be
> speed-shifted, but you need to figure out how much to shift it.
> Second, the frequency response of the printing process is not flat. According to
> "The worst print-through occurs at a wavelength equal to 27 * C. C is the total tape caliper in
> mils. For a typical 2
> mil mastering tape, the worst wavelength for print-through would be about 12.6 mils. When running
> at 15 ips, this
> would be a frequency of about 1200 Hz."
> Note: there's an error in their formula, as printed in the on-line document. It should read 2 *
> Pi * C. But they're correct that it's worst at about 1200 Hz. This is confirmed by the October
> 1980 JAES article "The Print-Through Phenomenon" by Bertram, Stafford and Mills. It includes a
> graph of print-through vs. frequency.
> BTW, this article also states that "print-through ... can be reduced if [the tape] is repeatedly
> rewound. The amount of print reduction ...can reach as much as 7 dB." In their tests, this
> required 6 rewindings. "The rewindings should be consecutive with an optimum storage time between
> rewindings to achieve maximum reduction. The optimum storage time may depend upon the individual
> Third, is the printing process linear or non-linear? The 3M document cited above says it's
> linear. Camras, in the 1988 edition of "Magnetic Recording Handbook", says it's not, and that the
> ratio of the original to printed signal varies with the level of the original signal. I think
> Bertram et al. are saying it is linear, but I must admit that I have not yet entirely digested
> this long, complex article. Hopefully it is linear, because modelling a non-linear transfer
> function will not be much fun.
> So.... If the printing process is linear, the other problems seem manageable. But it will no
> doubt require a fair bit of fiddling to get the cancellation signal lined up in time and amplitude
> with each objectionable echo.
> -- John Chester