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.
Audio Engineer Emeritus
The Crane School of Music
SUNY at Potsdam, NY 13676
"Great art presupposes the alert mind of the educated listener."
"A true artist doesn't want to be admired, he wants to be believed."
"If you design an audio system based on the premise that nothing is audible,
on that system nothing will be audible."
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.
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada 647 479 2800
Quality tape transfers -- even from hard-to-play tapes.