DBX Signal processing removal?

[sKiZo]

I imagine anything can be reverse engineered and/or emulated given the resources and expertise ...

That said, it's been 50 years now, and I haven't seen it happen yet ... successfully anyway.

Interesting aside ... even dbx doesn't know how it was done any more. I tried getting some info on the 3bx expander a bit back and they're pretty clueless about the older gear since Harman bought them out. Apparently a LOT went missing during the transfer of ownership.

 

[smurfer77]

The dbx circuit provides an output that is a function (be it HF pre-emphasis, dynamic compression or whatever, doesn't matter) of the input signal. If this function is known it is reversible using the inverse function. Whether this function is applied by a circuit on analogue signal, or by software/chip on a digitized representation of the analogue signal makes no difference; the discussion of digital vs analogue in early posts on this thread are erroneous.

For those not familiar with signal processing, maybe an example will help. Remember that original surround sound was encoded into 2-channels and decoded with analogue circuits on analogue signals (I have a giant 4-channel sansui analogue decoder which just has an analogue circuit to take some of the out-of-phase signal to the rear speakers and applies a time delay), but once appropriate technology became available the same mathematical functions of those analogue circuits were applied with software/on-chip directly (arguably with less artifacts) on digital signals. Or for a simpler example, consider an analogue 'processor' formed by a single capacitor. This is a extreme/simple example of analogue processing. You can do the same processing that the capacitor does, but in the digital domain, by knowning the function/response of the analogue circuit (in this case the high-pass filter of known frequency point and slope). Of course compression, delays etc are more complicated, but the principle is unchanged.

Haven't read the following webpage carefully, but might provide some fuel for thought if you are keen to do it in software. I will try this in using Izotope or Audition software, when i get around to ripping my collection to PC. The only way this wouldn't work is if there is some unknown/unpublished factors/function to the dbx circuit/function (which I haven't looked into yet so I can't say for sure but i bet some digging around will reveal all).
http://www.bobweitz.com/dbx_webpage/dbx.html

 

[sKiZo]

"For every complex problem there is an answer that is clear, simple, and wrong."
H. L. Mencken

And of course, the obverse holds true as well. Looking forward to seeing your solution, although I'd think it'd be waaaaaaaaaaay more complicated than just getting a for real decoder ... <G>

Long as we're contemplating the Rube Goldberg approach, bonus points if it includes the use of a Chevy Sonic!

 

[smurfer77]

Looking forward to seeing your solution, although I'd think it'd be waaaaaaaaaaay more complicated than just getting a for real decoder ... <G>

A solution is presented in the link I posted (caveats are discussed within). For dbx you will just need any software than has EQ and expander.

For sure it could be nice to just use the dbx decoder box, but then i have a few different tapes with different types of noise reduction and it could end up being useful to know how to do this in software instead of buying a box for each scenario. Also, if i buy some old decoder, I will likely spend the time to recap to make sure it's doing it's job properly (probably not necessary, but that's how i am). Lastly, I really need to start having some net outflow of components from my place...

Also not sure if you mean to say my analogues used for explantions are simple but wrong. They are not loose analogues for sake of linking ideas (which i hate the use of in academia, especially physics) but direct analogues.