Tom - is this better?
I couldn't agree more - some tapes we only get one good shot at, and the
aim has to be to preserve as much information as possible.
Cedar Retouch (now much imitated) is indeed a sort of audio photoshop
with a spectral display - time is the x-axis, frequency the y-axis and
amplitude the z-axis, done with colour. The things you can fix with it
(and the mess you can make if you are careless) are nobody's business -
dropouts, bumps, clicks, pre and post echo, some distortions, etc, etc.
I like it, use it all the time, and I paid for it!
The nice thing, as I've said, is that you can pinpoint the offending
noise in time and frequency, so the amount of original material you
modify is minimised - and often the print is greatest at two or three
spot frequencies. If you take those bits out, the ear can't hear the rest.
On 25/10/2013 11:53, Tom Fine wrote:
> Ted, any chance you could modify your comment style to put them up top
> or in-line with the previous text? Sometimes your comments are many
> page-downs away, at the bottom of a long thread.
> I have to agree with Ted on this point:
> "To use agressive and irreversible techniques on an analogue original
> is surely to be discouraged when other techniques are available."
> A tape with bad print-through is more likely than not to be old and
> maybe there are limited opportunities left to transfer it without
> major playback issues. So, a clean, high-resolution transfer should be
> made and then you can use copies of the digital file to try DSP
> remedies. I do doubt that analog remedies would be any more or less
> effective than DSP circa 2013.
> I did suggest in my first reply that one could attempt analog
> solutions to the problem, but I've changed my mind on that. I can't
> think of an analog tool that would work markedly better from today's
> sophisticated DSP "remedy" software. And the many playback passes
> required for experimentation might be very bad for an old source tape.
> Another thought that occured to me was try working in one of the
> spectral programs, like Sony Spectral Layers. I haven't had time to
> figure this kind of method out yet, but plan to investigate. I'm
> suggesting this because I noticed in an AES presentation that
> spectral-display information was used to show out artifacts of ancient
> splices were rendered inaudible without effecting the music content. I
> assumed that a spectral editor was used to identify and "heal" the
> splice artifact. Perhaps the Cedar program Ted recommended is just
> such software?
> -- Tom Fine
> ----- Original Message ----- From: "Ted Kendall"
> <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Friday, October 25, 2013 5:32 AM
> Subject: Re: [ARSCLIST] Advice needed on removing / minimizing tape
>> On 25/10/2013 05:40, John Chester wrote:
>>> 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 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
>> I routinely use Cedar Retouch for print-through problems, whether
>> pre- or post-echo, and usually find that removing the two or three
>> most prominent components is enough to push it back into the noise.
>> To use agressive and irreversible techniques on an analogue original
>> is surely to be discouraged when other techniques are available.