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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. >Comments? 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 http://www.aes.org/aeshc/docs/3mtape/printthrough.pdf "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 tape." 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