dbx problems

[Tim Gillett]

Does anyone, maybe Ethan, have any circuit or general info on dbx II NR units?

I have a recording which will basically track on one channel but not the other. I suspect the record encoder was not right as all my usual tricks to aurally correct the tracking have only been partially successful.

I'm told by the guy who initially did the recording it was recorded in 82 on a Teac X 10R with matching dbx II units.



I have a special interest in getting the recording right as it's my band that's playing. I'd totally forgotten that the live concert in 82 had been taped and it looks like it's the only surviving recording of the band in a non studio setting. As you might imagine, all of us former band members are pretty excited about the project.
Any info appreciated.

Once I get it sorted I hope to post a small sample for you to hear.

cheers Tim.

[evm1024]

No DBX II schematics here just the DX-4D

http://arafel.org/audio/manuals/dx4dsch.pdf

Good luck!

[evm1024]

Take a look here: http://members.tripod.com/~coreyeng/dbx1.htm

Some type II schematics (or so they say...)

Enjoy

[The Ghost of FM]

Which dbx II unit are you using to decode this recording?

[Tim Gillett]

Originally Posted by evm1024

Take a look here: http://members.tripod.com/~coreyeng/dbx1.htm

Some type II schematics (or so they say...)

Enjoy

Thanks Ethan, I'll check them out. Tim

[Tim Gillett]

Originally Posted by The Ghost of FM

Which dbx II unit are you using to decode this recording?

Just for starters I tried the ones in a Teac V-5RX consumer cassette deck I had on hand, patching in to the dbx units independently of the rest of the deck's audio. I smelt a rat when even after swapping dbx channels I got exactly the same problem with the tape's left channel, suggesting the dbx boards I was using are probably OK. But then again...

The guy who made the recordings still has the original dbx units. Dont know the model no's and he'd promised to get the actual units to me, although that may not be for weeks. But he also said he had problems with them way back then, so that's not encouraging and suggests possibly an encode problem.
Does anyone know the model numbers that would normally be used on the X 10R?

thanks Tim

[dementedchord]

Originally Posted by Tim Gillett

swapping dbx channels I got exactly the same problem with the tape's left channel, suggesting the dbx boards I was using are probably OK.
suggests possibly an encode problem.

thanks Tim

sorry but there it is... even if the unit's you played back through were'nt exactly the right ones they should have "tracked" the same and played back relitively cool... how does the bad side sound with out the decode enabled??? perhaps you could run that side through a multiband comp??? that way you could smooth it some and then add some gain...

[The Ghost of FM]

Originally Posted by Tim Gillett

Just for starters I tried the ones in a Teac V-5RX consumer cassette deck I had on hand, patching in to the dbx units independently of the rest of the deck's audio. I smelt a rat when even after swapping dbx channels I got exactly the same problem with the tape's left channel, suggesting the dbx boards I was using are probably OK. But then again...

The guy who made the recordings still has the original dbx units. Dont know the model no's and he'd promised to get the actual units to me, although that may not be for weeks. But he also said he had problems with them way back then, so that's not encouraging and suggests possibly an encode problem.
Does anyone know the model numbers that would normally be used on the X 10R?

thanks Tim

I'm not sure if TEAC offered their own branded dbx unit for their consumer open reel decks back then but an outboard dbx type II unit would include the 224/224X and the NX-40.

The 224 series units had stereo calibration controls accessible from the outside of the units on the front or rear apron depending on the model.

I'm also suspecting that the original deck the tape was recorded on my have had other issues beyond a poor encoder...perhaps the deck was out of mechanical alignment or with worn or dirty heads that botched up the initial recording?

I can't recall ever reading or hearing much about a dbx unit itself being defective as their reliability record was pretty near perfect.

About all you could really do is tweak the repro level up and down for that channel to try and get back to the 0db reference point where the dbx process should work at its most transparent level and if it's still messed up at that point, you'll need to look at other fixes like making a mono track of the good side and losing the pooched one.

Cheers!

[Tim Gillett]

Thanks Jeff,

Good to know dbx's had such a good track record (no pun intended).

The tape is interesting in that recorded on an X 10R where side 1 was recorded with the side 1 head and side 2 with the reverse side head. Interestingly the side 1 left channel is especially low and difficult to track. On side 2, with a different record head used, the problem isnt nearly as bad. I agree, it had to be at least an alignment problem otherwise why is side 2 not nearly as bad?
Another thing is the record levels seem to have been pushed quite hard, totally unnecessarily IMO as dbx already lifts the quiets up a hellava lot, way above tape hiss, but it means my dbx decoders are close to clipping just to track properly.
i've also wondered about another potential problem. What happens when the encoder runs out of compression at high levels? Does it just pass the signal on uncompressed? Does it clip? Or both? Whatever, that might mean the decoder now is trying to expand a signal that , at that point in the range, was never compressed, and so you get unnatural expansion of a signal that doesnt need expansion, if you know what I mean.
That would tally with what I'm hearing. It tracks well at middle and lower levels but voice peaks blast at you, bringing the whole mix up for that moment, and then it settles down again. I can sort of deal with it using a bit of careful compression on just these peaks but a whole lot better to try and sort it at the source IMO.

Thanks for your comments.

Tim

[The Ghost of FM]

but it means my dbx decoders are close to clipping just to track properly.

But you're referencing your statement to the dbx circuitry that's built into your cassette deck and you may find that the outboard 224/224X series units may offer more headroom before they clip because they were designed to work with open reel decks running at hotter levels then what's presented on a consumer cassette deck.

If you can get your hands on a 224/224x, you might find your recording is more salvageable then what's in your mind right now with its current sound quality.

What happens when the encoder runs out of compression at high levels? Does it just pass the signal on uncompressed? Does it clip? Or both?

I don't believe the compression can get to a state where it runs out of compression and passes through an unprocessed signal...it's not that smart of a device to do that!

It basically will just clip and induce more tracking errors and it won't sound pretty.

To avoid this kind of trouble, the engineer basically has to do his/her job in the first place and that means watching your levels.

Cheers!

[Tim Gillett]

Agree. My best shot is to wait for the proper dbx units and take it from there.
It may be as you say the tracking problem (or the ugly expansion one at least) is no longer there with a better decoder. At least I'm satisfied the recording is good enough to persevere with.

Cheers and thanks for the comments, Tim