Old 09-06-2010, 02:33 PM   #1
pac-man
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Default Dolby A/B/C spec anyone?

I believe it to be some kind of dynamic EQ + compression + expansion.
Does anybody know how it works, more specific?

(I'd like to mimic it in Reaper)

Thanks
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Old 09-06-2010, 02:55 PM   #2
chriscomfort
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I personally don't know anything about it but I found this http://en.wikipedia.org/wiki/Dolby_A
Seems like a pretty thorough start.

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Old 09-07-2010, 02:52 PM   #3
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I've seen this discussed before (on other forums) and from what I've read, it looks like the exact details are a trade secret and you'd have to get a license from Dolby to obtain the algorithms. (i.e. I've never seen anything published about attack/releast times.) The patents should have expired by now, but I guess trade secrets don't expire.

If for some reason you just wanted to create something similar that doesn't need to be exactly compatible with existing tapes, you could choose your own atack/decay, thresholds, ratios, shelving frequencies, etc., and that should be fairly "easy"! (I kinda doubt that's the situation...)

Apparently, some people have reverse-engineered it (at least Dolby B), and if you search for "Dolby B plug-in" you'll get some hits. If you have a tape player with the encoder/decoder, you could probably approximate it (with a fair amount of tweaking & trial-and-error). But if you only have an encoded tape and no reference decoder, it would be more difficult to get it right.

...I remember there was one problem where someone had a cassette without Dolby NR that was accidently digitized with Dolby turned-on (on the cassette player). IIRC, there was no solution except to "fix it" as much as possible with EQ. (I don't remember the whole story... I don't remember why the original tape was not available to start-over with Dolby off.)

If you have some dolby encoded analog tapes, the best solution is to find a tape machine with the proper decoder, or find someone with the proper machine and have them digitize the tapes for you.
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Old 09-07-2010, 03:53 PM   #4
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Dolby A/B/C were noise reduction systems employed on Tape decks/machines to remove hiss/background noise.They are pretty much redundant in the digital domain because of the much better noise floor.

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Old 09-07-2010, 04:05 PM   #5
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Dolby noise reduction is a loopback system. The specs are freely available, though why someone would want to write a plugin for it I don't know.

First of all, use the tape deck that recorded the tape, for playing it back. That way, your repro/rec head will be aligned properly, because almost no tape deck is adjusted the same way.

When professional 1/4 up to 2 inch tape was used, the decks were calibrated pretty much before each session. This is obviously somewhat beyond the home user with an 1/8 inch cassette tape that carries four tracks(stereo on a-side and b-side).

Most of my 20 year old tapes play rather well, but only on the tape deck I made them with.

Some information can be had here, a great Wikipedia article and the PDF from Dolby themselves.
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Old 09-08-2010, 01:56 PM   #6
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Quote:
...though why someone would want to write a plugin for it I don't know.
Maybe you don't have a machine with the proper decoder. Or maybe you no longer have the original tape and somebody digitized it without decoding.

Or as I mentioned above, someone might have digitized a non-Dolby tape while processing thru a dolby decoder and you need to reverse it.
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Old 09-12-2010, 07:41 AM   #7
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Thanks for the answers

I'm really only after it for the sound, i'd like to use it as an effect.
I'll probably look for an old "real" encoder/decoder unit instead...

The plugins that i've stumbled upon are synthedit, which unfortunately doesn't work for me...
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Old 07-26-2013, 08:26 AM   #8
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Quote:
Originally Posted by airon View Post
Did anyone grab this PDF? -(old thread I know but the search function is a mine of information) - seems to have been removed since then.

Cheers,
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Old 03-27-2021, 02:04 PM   #9
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http://tka4.org/materials/lib/Articl...on_Systems.pdf

Here'ya go.
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Old 03-27-2021, 02:21 PM   #10
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Quote:
Originally Posted by pac-man View Post
Thanks for the answers

I'm really only after it for the sound, i'd like to use it as an effect.
I'll probably look for an old "real" encoder/decoder unit instead...

The plugins that i've stumbled upon are synthedit, which unfortunately doesn't work for me...
https://www.audiothing.net/effects/type-a/
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Old 03-27-2021, 02:50 PM   #11
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Found some info about Dolby A on Gearslutz
https://www.gearslutz.com/board/low-...-deck-mod.html
And there is really doable trick in Reaper from S.O.S. originally for Cubase
https://www.soundonsound.com/techniques/bright-idea
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Old 03-30-2021, 07:04 PM   #12
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I asked a similar question about a week ago because of this video:

https://youtu.be/ZRP5uI9mbzQ

My conclusion is that the effect is nearly unique to the analogue/magnetic tape realm. The tape plugin in Worrell's video has managed to recreate the routing of Dolby systems and multi-tracks.

U-He Satin available here: https://u-he.com/products/satin/

You could also try this:

https://youtu.be/H-Gs-o39C5o
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Old 03-31-2021, 12:56 AM   #13
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The audiothing "type-A" sounds really good. If you want a rough approximation for giving your backing vox that 70's sheen, then you can have a go with something like the attached fxchain...
Attached Files
File Type: rfxchain FakeDolbyATrick_V4.RfxChain (1.1 KB, 58 views)
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Old 03-31-2021, 07:37 AM   #14
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Quote:
The audiothing "type-A" sounds really good.
OK... But it wasn't originally an "effect". It was a closed-loop noise reduction system for analog tape.

Recordings made and played-back with Dolby had less tape hiss than those made without it. Otherwise they sounded the same.

If it was used for recording-only or playback-only the sound would be altered/degraded. There have been "reports" of older Dolby-A tapes that were not decoded when digitized for CD but I'm skeptical... The good-reliable studios would have labeled the tapes.

If you had a Dolby B cassette it would play "brighter" (boosted high frequencies) when played-back with Dolby turned-off (or on a tape deck deck without Dolby) and some people liked it that way. But it wasn't supposed to be used that way.

Of course, digital recordings don't have tape hiss so it's not needed.
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Old 03-31-2021, 10:14 AM   #15
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Quote:
Originally Posted by DVDdoug View Post
OK... But it wasn't originally an "effect". It was a closed-loop noise reduction system for analog tape.
No, but neither was tape delay. It's just another one of those happy accidents where someone screwed up and they realized that it could be used creatively.
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Old 03-31-2021, 04:39 PM   #16
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Quote:
Originally Posted by DVDdoug View Post
OK... But it wasn't originally an "effect". It was a closed-loop noise reduction system for analog tape.
Yes. I know. More here:
https://www.audiothing.net/blog/the-dolby-a-trick/
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Old 03-31-2021, 04:58 PM   #17
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The thing Dan Worral showed (kirk1701’s reply above, and I sort of suspect what triggered the OP question) was all about how non-linear processes respond differently when you wrap this type of frequency dependent compansion around it than if you just keep things flat and with full dynamics all the way through. It IS a special effect which can’t really be achieved other ways, but has absolutely nothing to do with noise reduction.

Edit - also as I mentioned in kirk’s thread, you can get pretty close with a pair of ReaXComps and appropriate settings, which I assume is why we’re looking for the appropriate parameters.
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Old 03-31-2021, 05:42 PM   #18
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See also https://forum.cockos.com/showthread.php?t=230566

I've now got 5 different versions kicking about on this computer. I should have just shelled out my €59 and bought the Audiothing.
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