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ARSCLIST  April 2013

ARSCLIST April 2013

Subject:

Re: remanence decay and tape aging

From:

"Richard L. Hess" <[log in to unmask]>

Reply-To:

Association for Recorded Sound Discussion List <[log in to unmask]>

Date:

Wed, 17 Apr 2013 20:53:46 -0400

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text/plain

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text/plain (84 lines)

Hi, Gregorio,

I subscribe to the "just bad recording" theory, to be honest. Why did 
they put that lamp there? Did you really need to have the lamp flashing? 
but not too brightly? Oh the meter--how do you use that 
<smile><sigh><groan>.

Print through happens as the thermal idiot particles that have very low 
remanence will flip and they can be biased perhaps by the earth's 
magnetic field. They are the ones that cause crosstalk. Most of the 
particles do not crosstalk. This is why low-level erasure will reduce 
crosstalk, but it has never been deeply perfected and most of us are to 
scared to try it...even if we had machines that implemented it.

Cassettes possibly show a loss of magnetic record at high frequencies, 
but that has never even been seen on reels. The mechanism on cassettes 
is not well understood and the sightings were never followed up. I've 
never measured them.

Sorry I cannot be of more assistance with definite answers.

Cheers,

Richard

On 2013-04-17 5:20 PM, Gregorio Garcia Karman wrote:
> Hello Richard,
>
> many thanks for your answer.
>
> At least intuitively, I would have thought that the magnetization of a tape—if given enough time—would eventually relax to 0. I ask because I have occasionally come across amateur recordings from 1950s and 60s whose signal would seem to be nevertheless too faint, whereas others in the same lot seem to have survived the passing of time crisp and fresh. Those low-level tapes didn't seem to be affected by SSS, SBS, etc. but of course it is also quite possible that they were very bad recordings in the first place.
>
> However... do you think we could consider print-through as the that ferromagnetic particles do get reoriented to an audible extent even in the presence of small magnetic fields? Also, I don't know if anyone had this experience too but picking up some of my old cassette recordings I would have sworn that the SNR was getting worse than the digital ear would have expected. On the other hand, I guess cassette tapes have lower coercitivities and slow chemical degradation is probably always there even if it can't be ascribed to one of the common "tape diseases".
>
> One way or the other I was interested in finding out if any of those aging effects could be quantified in terms of signal attenuation or SNR loss. Thanks for forwarding the question. Will keep my ears open.
>
> Best regards
>
> Gregorio Garcia Karman
> [log in to unmask]
>
>
>
> On 17.04.2013, at 19:01, Richard L. Hess wrote:
>
>> Hello, Gregorio,
>>
>> In general, the magnetic record seems to be rather robust and it mostly decays from close encounters with magnetic fields stronger than the Earth's. I know of no studies that have attempted to quantify this, but I'm copying Jay McKnight who may know of a study and if he has any information, I'll post it to the list.
>>
>> So, assuming no chemical or physical degradation (which mostly affect tape via spacing loss across part or all of the tape) and no close encounters of the strong magnetic kind, the S/N decay rate would be minimal (I don't want to say zero, but I suspect close to it).
>>
>> We had the discussion on the Studer list about whether tape or machine background noise is predominant and Jay chimed in with an "it depends". For master tapes, generally the tape noise is predominant. There are times at slower speeds and narrower tracks where head/electronics noise would be predominant.
>>
>> As to degradation factors, I have a page I try and keep updated where this is discussed.
>>
>> http://richardhess.com/notes/formats/magnetic-media/magnetic-tapes/analog-audio/degrading-tapes/
>>
>> I hope this helps a bit.
>>
>> Cheers,
>>
>> Richard
>>
>>
>> On 2013-04-17 12:32 PM, Gregorio Garcia Karman wrote:
>>> Dear members,
>>>
>>> I am looking for references in the literature dealing with the study of the decay of magnetic remanence as an effect of tape aging. What is the expected signal-to-noise decay rate under ideal conditions (i.e. no chemical degradation)? In real life, what is your experience in regard to different brands / models in similar storage conditions?
>>>
>>> Thanks in advance and regards
>>>
>>> Gregorio
>> -- 
>> Richard L. Hess                   email: [log in to unmask]
>> Aurora, Ontario, Canada                             647 479 2800
>> http://www.richardhess.com/tape/contact.htm
>> Quality tape transfers -- even from hard-to-play tapes.

-- 
Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada                             647 479 2800
http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.

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