The wonders of modern DSP in careful craftspeople's hands!
The next frontier will be figuring out how to grab the just musical content out of a noisy grooved
disk and then un-do the problems of groove distortion and disk wear. I hope Carl Haber's work leads
there -- scan the groove and then come up with some kind of Photoshop-like algorhythm to "heal"
groove wear and the material on the groove surface that produces playback noise (I'm assuming that
comes down to rough-surface shellac, which would need to be differentiated from minute lateral
changes in the groove, ie soft-dynamic music content). I am optimistic that such a system will
emerge in my lifetime. Imagine few-dozen-dollar software that enables you to scan your 78RPM disks
on a high-resolution flatbed, then "heals" the ravages of time and the problems with the original
shellac compound and saves a clean,crisp audio file to your hard drive.
-- Tom Fine
----- Original Message -----
From: "Ted Kendall" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, October 25, 2013 7:56 AM
Subject: Re: [ARSCLIST] Advice needed on removing / minimizing tape bleed-through
> 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 bleed-through
>>> 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.