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ARSCLIST  July 2019

ARSCLIST July 2019

Subject:

Re: Preserving both raw and decoded files for tapes recorded with Noise Reduction?

From:

"Casey, Michael T" <[log in to unmask]>

Reply-To:

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

Date:

Tue, 16 Jul 2019 20:56:20 +0000

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (179 lines)

Hi Richard,

At Indiana University's MDPI project, we create a preservation master file 
that is the raw, undecoded output and a preservation master-intermediate file 
that is decoded. You are not alone! Both are created at the same time during 
one pass. We believe that both are needed for accurate preservation of the 
content. By keeping the undecoded version, we hold open the possibility of 
redoing in the future the highly subjective and often inaccurate choice of 
which Dolby (or no Dolby) to use and how much gain to apply before the Dolby 
circuit. This meets a basic media preservation principle around the nature of 
judgment calls, where they are viewed as potential weak links in the 
preservation chain. This leads to our policy to preserve not only the 
subjective product of a judgment call, but also a product that is not the 
result of subjective decisions.

More information on how we handle Dolby-encoded cassettes is on our blog:

https://blogs.iu.edu/mdpi/

Mike

---------------
Mike Casey
Director of Technical Operations, Audio/Video
Media Digitization and Preservation Initiative
Indiana University

https://blogs.iu.edu/mdpi/
https://mdpi.iu.edu/




-----Original Message-----
From: Association for Recorded Sound Discussion List 
<[log in to unmask]> On Behalf Of Richard L. Hess
Sent: Sunday, July 14, 2019 8:53 PM
To: [log in to unmask]
Subject: [External] Re: [ARSCLIST] [EXTERNAL] [ARSCLIST] Preserving both raw 
and decoded files for tapes recorded with Noise Reduction?

This message was sent from a non-IU address. Please exercise caution when 
clicking links or opening attachments from external sources.
-------

Hi, Corey and Gary,

Thanks for your kind remarks about the decoder. My colleague and friend, John 
Dyson has done a wonderful job with the code. His acid tests have been leaked 
Dolby recordings of 70s pop music--some of them sound so bad until he decodes 
them...but they are tougher than the stuff I've recorded and obtained from 
other sources.

What has happened is the intermod that is normally generated by fast gain 
changes on decoding is vastly reduced.

As to my question, am I the only proponent of recording the raw, undecoded 
output? It's saved my bacon more than once, and I've been insisting on it for 
at least a decade. I was hoping that some standards/best practice body 
recommended it. I did not think I was alone.

John Chester, thanks for the info on 384 kHz sampling frequency and bias.

Remember my effort here?
http://richardhess.com/notes/2008/02/02/tape-recorder-bias-frequencies/

The only major recorders that are problematic (i.e. bias frequencies above 180 
kHz are:

Ampex ATR-100 (432 kHz)
Sony APR-5000 and probably multitracks (400 kHz) Studer A80VU (240 kHz, most 
late models are 150 or 153.6 kHz,
               the A77 is 120 kHz)
Otari MTR-10/12 and MTR-90 (246-250 kHz)

Cheers,

Richard


On 2019-07-14 7:16 p.m., Gary A. Galo wrote:
> Hi Richard,
>
> I echo Corey Bailey's email in congratulating you on the software-based NR 
> decoder. I'm sure there will be a considerable market for it.
>
> The issue of preserving the "original" data - whether analog of digital - is 
> a sticky and controversial one. When I gave my ARSC presentation on 
> transferring PCM-F1 format digital recordings for the NY ARSC chapter April 
> 2018, I was taken to task by one attendee for not preserving the original 
> bits. I go from the S/PDIF output of my PCM-601ESD digital processor 
> directly into a Tascam DA-3000 digital recorder. The Tascam has a built-in, 
> switchable sample rate converter based on the Cirrus Logic CS8422 SRC chip 
> (which doubles as the S/PDIF input receiver). I set the Tascam to record at 
> 88.2 kHz, so the CS8422 is converting 44.056 to 88.2. An "undocumented 
> feature" of the DA-3000 recorder is that the CS8422 SRC chip also does 50/15 
> uSec de-emphasis, which take care of another issue with F1 recordings. Why 
> Tascam fails to mention this anywhere in their manual or product literature 
> is beyond me, because the de-emphasis feature is clearly stated on the front 
> page of the CS-8422 data sheet, and it's an extremely useful feature.
>
> With this method, only the inter-channel time delay and DC offset still need 
> to be addressed once the 88.2 kHz data is on your computer.
>
> My method does not save the original 44.056 kHz bits. Guilty as charged. 
> But, the CS8422 does a beautiful job with the SRC and the de-emphasis, and 
> has ultra-low jitter clock recovery to boot, so I sleep well at night. If 
> you feel the need to preserve the original bits, you could run a second, raw 
> transfer directly into your computer, if your computer will lock onto 44.056 
> kHz. Or, you could use a digital distribution device to split the 44.056 kHz 
> data stream, sending it to both the computer, and the DA-3000 recorder 
> simultaneously. But, I just don't see the need.
>
> So there is no misunderstanding, I can well understand the desire to 
> preserve the non-decoded Dolby-A analog signal in case better software 
> conversion becomes available down the road. It makes sense to do this. So, 
> perhaps I'm being inconsistent. These are thorny issues, and everyone will 
> have their own viewpoints.
>
> Best,
> Gary
>
> ____________________________
>
> Gary Galo
> Audio Engineer Emeritus
> The Crane School of Music
> SUNY at Potsdam, NY 13676
>
> "Great art presupposes the alert mind of the educated listener."
> Arnold Schoenberg
>
> "A true artist doesn't want to be admired, he wants to be believed."
> Igor Markevitch
>
> "If you design an audio system based on the premise that nothing is
> audible, on that system nothing will be audible."
> G. Galo
>
> -----Original Message-----
> From: Association for Recorded Sound Discussion List
> [mailto:[log in to unmask]] On Behalf Of Richard L. Hess
> Sent: Sunday, July 14, 2019 5:42 PM
> To: [log in to unmask]
> Subject: [EXTERNAL] [ARSCLIST] Preserving both raw and decoded files for 
> tapes recorded with Noise Reduction?
>
> Hi, I think many of us agree that it's necessary to preserve both the
> raw transfer and the decoded version of a file which has been recorded
> with Dolby or DBX type noise reduction.
>
> When I first thought about it, I never imagined I'd be part of a team
> that would produce a better decoder for Dolby A encoded tapes than
> Dolby, but it's happening and humbling... So, it is a good idea to
> save as much raw data as possible because who knows what else will come 
> along.
>
> Plangent is wonderful, but a bit problematic as it is still
> inconvenient to properly archive the bias, but that's another story,
> and I think in the long run it would be good if we could do that.
>
> MY QUESTION is: Are there any standards or recommendations that say
> "keep the raw undecoded copy as well as keeping the decoded copy?
>
> It's for a paper that Federica and I are writing.
>
> Thanks!
>
> Cheers,
>
> Richard
>

-- 
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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