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Hi Tom - Seems there is no simple answer. Reminds me of the way the Motors auto repair manuals would begin describing the process of rebuilding a motor: "With engine on bench..." Thanks for your comment. Malcolm ******* On 10/25/2013 7:32 AM, Tom Fine wrote: > Hi Malcolm: > > I think click and pop removal software looks for level spikes of short > duration, not for repetitive patterns. I don't think time between > ticks and pops matters, it's more spike duration and percent above > average level. This is why if you over-use that kind of DSP, it > squashes percussives like drum hits. I have to admit that there are > some de-click tools that now really just remove ticks. Pops are still > too long duration, and all software I've tried or gotten test examples > of leaves artifacts on the underlying musical content. Pops can be > dealt with more easily in spoken-word and other less-complex sound > environments. Ticks are of such short duration that you can spank them > down and the mind will fill in the tiny void, as long as the void is > tiny enough and the ticks aren't spanked down lower than the > surrounding music level so a "white void" is created (the "white > voids" are very noticeable). The guy who figured out how to scrape off > a little bit of oxide to reduce tick levels on tape dubs (was it John > R. T. Davies?) figured this out decades before DSP. The guys who used > to make tiny deletions of the tape where the tick peak was were > messing with the time-domain, which is noticeable to people with a > good sense of rhythm and most other careful listeners. The > oxide-scraping method leaves the time domain intact but messes with > the amplitude of a microsecond of time, which is less noticeable to > the listener because the brain can fill in the tiny amount of missing > content. > > Of course, the very best method I have heard for fixing a tick and > even shorter-duration pops is to use the waveform editing tool and > simply draw out the spike, freehanding in the missing waveform. It's a > skill, but it can be learned by people not good at drawing with > pencils like myself. You can't tune tick removal software to do this > right all the time, because you're tuning it to reduce ticks to a > certain level, not to re-draw the wave where the tick was, following > the contours before and after. I betcha spectral editing could come > pretty close, though. You'd "heal" all the elements of the tick except > those exactly in the content frequencies. > > -- Tom Fine > > ----- Original Message ----- From: "Malcolm Rockwell" > <[log in to unmask]> > To: <[log in to unmask]> > Sent: Friday, October 25, 2013 12:59 PM > Subject: Re: [ARSCLIST] Advice needed on removing / minimizing tape > bleed-through > > >> Seems a variable delay time algorithm has already been written, else >> how would one de-click a 78 that has a repeating click across the >> grooves at, say, 90 degrees (like a scratch or a repaired broken >> record)? Same algorithm, different application. >> Ted Kendall's idea of "removing the two or three most prominent >> components (of the echo signal being) enough to push it back into the >> noise" is a good one, as well. >> And, of course, we never fiddle with the analog master. There should >> be no need to if it is intact and can play through. >> Malcolm >> >> ******* >> >> On 10/25/2013 12:41 AM, Tom Fine wrote: >>> 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. >>>>> 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 >>>> >>>> >>> >> >> >