Print

Print


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
>>>>
>>>>
>>>
>>
>>
>