DBX Type II N/R decoding

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Gene Pink

Well-known member
Joined
Aug 9, 2015
Messages
626
Location
Austin, Texas
Is there a plug-in out there for modern DAW's, that can decode this with reasonable accuracy?

I have a 1/2" 8-track from 1983 of my old band, recorded on the usual ubiquitiusTeac or Tascam of the time with this N/R encoded. A friend has a suitable working deck, but not a way to decode this N/R, and it seems to be a rather complicated algorithm. He uses Cubase.

Any ideas would be appreciated, thanks.

I'm trying to cross another item off of my bucket list.

Gene
 
Gene Pink said:
Is there a plug-in out there for modern DAW's, that can decode this with reasonable accuracy?

I have a 1/2" 8-track from 1983 of my old band, recorded on the usual ubiquitiusTeac or Tascam of the time with this N/R encoded. A friend has a suitable working deck, but not a way to decode this N/R, and it seems to be a rather complicated algorithm. He uses Cubase.

Any ideas would be appreciated, thanks.

I'm trying to cross another item off of my bucket list.

Gene
I don't know how complicated,

IIRC it uses full range 1:2 expander, with 12dB of HF de-emphasis (between 500Hz-2kHz). They hype using RMS detector, but I don't know how much of an audible difference that makes, I recall seeing some DBX mimics  using  average detectors that sounded very similar.

JR
 
nielsk said:
They seem to be going for around $50... may be a whole lot easier and cheaper to just use the hardware?
Are they going that cheap? I had no idea, I thought they would be rare and pricey. Time to search ebay., thanks.

And can always resell, after this one-time use.

Gene
 
I gave away a DBX rack with DBX Type II NR just the other day to a member here!  He was more interested in the rack so he might be happy to part with a few cards.  Let me check, you'd have to get the pinout and wire manually to the edge connector but it's easily done.

 
Yes I do have them, and am mostly planning on mining the rack for parts in a 500 series build, so if the cards would be of better use elsewhere I would be happy to figure out how they can head the way of someone who could make use of them.
 
nedonnelly said:
Yes I do have them, and am mostly planning on mining the rack for parts in a 500 series build, so if the cards would be of better use elsewhere I would be happy to figure out how they can head the way of someone who could make use of them.
That would be cool, stand by for a PM.

How many do you have, and what format are they? I have an empty 800 series 10 hole Valley People rack with PS that may make things easier on my end.

I don't expect these for free.

Gene
 
I have 3 empty DBX 208 NR racks, PSU's are still there and also wiring looms that are the multi-pin on one end and XLR on the other.  XLR's are rough, but may work fine.  The racks had 411 cards in them originally.  Up for grabs if of use; whatever my time is worth to pack a big box.  You may find similar with cards on ebay for nearly nothing as well. 

A 208 rack and a 900 rack are pretty much the same thing, except for one mechanical rail that keeps 900 series cards from fitting in.  400 series cards fit and work in a 900 rack. 
 
Gene Pink said:
That would be cool, stand by for a PM.

How many do you have, and what format are they? I have an empty 800 series 10 hole Valley People rack with PS that may make things easier on my end.

I don't expect these for free.

Gene

Hi Gene,

I gave the rack to Nedonelly last week.  It's a 900 series rack.  I never tested the Type II cards, they were in the rack when I bought it. 

A quick google search says that Valley 800 and DBX 900 are not compatible, different pinout…

I may have a pair of edge connectors lying around, you could lash up a +/- 15V supply from a bench supply if you have one.  If not I probably have a power one +/- 15V supply I could scare up too.
 
emrr said:
I have 3 empty DBX 208 NR racks, PSU's are still there and also wiring looms...

PM will be sent.

I gotta say, it is amazing the way people have stepped up here to help out someone they don't even know.

So far. what I learned about DBX, and anyone feel free to correct me, is that 800 vs 900 racks are completely different, while the blank faceplates may be the same size, the edge connector is way different, 15 pin on the 900, and about 30 pin on the VP 800. Don't know if the overall depth, or even if the connector is in the same position. I guess it doesn't matter, there is no easy "goesinta" solution involved here. My spare VP 800 rack is useless for this. A jpeg in my post from last year that shows an empty 800 rack:

https://groupdiy.com/index.php?topic=62463.msg791537#msg791537

The 941/941A cards are for encoding to tape, and the 942/942A cards are for decoding from tape, what I need. Each card is stereo, didn't know that. Is there an audible difference between the 942 and the 942A?

Now I gotta get ahold of my friend with the Tascam  to see if he is still into doing this, he moved from central TX to Idaho last year. Everything involves shipping, which is why I was first leaning toward a Cubase plugin solution. Ship a tape, or ship a tape along with 8 ch of analog DBX II N/R, ready for him to go.

One other thing, do these cards need to be calibrated to a test tone for some threshold level, or do they just do their thing at any level?

Thanks to all,
Gene



 
Do these NR cards age well?
I dont know whats involved in calibration but el caps are likely drifted or leaky.

Plugin idea makes sense--Does anybody still use max/msp or whatever it has become?
 
It might be easier to have him do the transfer with the tracks still encoded (compressed) and you can decode them later... That will eliminate some complexity at his end...  This should not hurt your ultimate end result.

JR
 
DBX is very frequency sensitive.  Hopefully you have hi mid low tones.  The flatter the playback the better the tracking decode.  Dolby is more tolerant of frequency but needs level accurate mid frequency as does DBX.  Mistracking  Is the main problem with NR.  Make sure you transfer tones if you choose to transfer and decode later. 
 
fazer said:
DBX is very frequency sensitive.  Hopefully you have hi mid low tones.  The flatter the playback the better the tracking decode.  Dolby is more tolerant of frequency but needs level accurate mid frequency as does DBX.  Mistracking  Is the main problem with NR.  Make sure you transfer tones if you choose to transfer and decode later.
In my experience Dolby was the more twitchy than dbx .... Dolby mistracks if the encode/decode amplitudes are not matched. (I was over manufacturing a 4T cassette with dolby C and that was a huge PIA.)

dbx is a 1:2 expander so frequency response errors (for simple tones) are expanded 2x. IIRC the side chain is bandpassed so extreme response errors are somewhat mitigated. Dolby (below threshold)  will also expand errors 2x. 

No free lunch in Tape NR...  but if you print it still compressed you can EQ those response errors before decoding to avoid expanding them.

JR
 
I'm thinking dolby A with 4 band processing. 10 DB  broadband and 15 DB in top end.  DBX  was 25 to 30 DB processing.  Any tape playback errors were way more noticeable with mistracking on DBX. And frequency problems with bumps and peaks create problems elsewhere with that much processing.  Dolby A with 4 bands would not effect high bands when the problem was a low frequency head bump but you would here it right away on DBX with full band processing.    I remember setting up an Otari 1 inch 8 track with DBX 408 or something like that and it sounded so much better than I had heard before.  It was because the frequency response was very Flat when playback and record were calibrated.  I always felt the cheaper Tascams at that time usually had no low play back to compensate for head bumps with tape and IPS (thing of Tascam 1/2 inch 8 track). DBX would mistrack and make topend sound over expanded or compressed.
 
Update:

I heard back from my friend, when his extended family got together fir the holidays, he gave the Teac 80-8 to his brother, it now resides in Las Vegas.  :'(

He did find a possible software solution that covers Dolby and dbx: encode/decode:

http://www.u-he.com/cms/satin

He can't vouch for it, but at least it is a possibility. Thanks to all that stepped up to help.

Gene

 
Satin looks promising.  I have a pair of Dolby 361 A type for decoding old tapes. It would be nice to compare.
 
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