Multiband Compressor/Expander/leveler OTT Compression in Hardware

[djdonovan]

Hi all. This is my first post and I am not an electronics engineer, but I like to tinker. Disclaimer: This is a rabbit hole I have been falling into recently that would beg the question "why the hell would you want to do that". Despite that, there is an effect that I am going after that I'd like to do in the analog/hardware/live domain, hence my research.

Is anyone aware of a hardware multi band compressor that has auto makeup gain or expansion? I've done some searching and I have come close to a couple things that are done full band such as a dbx (model eludes me at the second) and the Valley People Dynamite. My interest is in recreating the effect that is created ITB by multi band plugins that have the "Over The Top" setting (in Ableton's MB compressor), or more specifically by Xfer Records OTT multi band compressor plugin.

In my mind wiring up 3 Valley People TA-101 VCAs through 2 selectable crossovers/3 bands and back to a summing mixer might do the trick, but again I'm making a lot of assumptions on the feasibility of the electronics circuitry. I've also considering the idea of using a crossover to split the signals into 3 compressors/expanders, then mixing back together. I've also heard mention of parallel compression used to get the effect of expansion. I'm not so concerned about the noise floor as this is part of the effect, but it would make sense to have some sort of gating logic when the effect is used with extreme settings. If Steve Duda ever got into hardware I would hope this would be his first product  ;D

I'd be willing to taking a stab at this on a breadboard, but I also don't want to reinvent the wheel.

I'm also looking for a good 500 series module that does this in the single band that has sidechaining and the Valley People Dynamite seems to fit the bill (which led me to their VCA's).  At the very least this has provided an interesting look into the history and mechanics of compression and products over the years!

Cheers,
Donovan

 

[Rob Flinn]

This has been discussed before if you do a search.  From memory I think the general concensus was that it is a lot more difficult to get it working righ than than it would appear on paper.

 

[djdonovan]

Thanks Rob, I'll search through the posts a little deeper. Curious to understand more.

Update: So far it looks like the Maselec MLA-4 might have the (expensive) features I am thinking of.  I also wonder if the effect I am going after actually requires two MLA-4s in parallel with one in compression mode and one in expansion mode. Expensive X 2 

To Rob's point, I can't imagine this discussion having not come up before. If I find any further info, I will update this thread in case anyone else stumbles across it.

 

[topcat]

Hi,
There are lots of interesting resources to help, try looking at broadcast processors or the dbx 3bx3bx
ftp://ftp.dbxpro.com/pub/PDFs/discontinued/Service%20Manuals/3bx%20Service%20Manual.pdf
Aphex 2020....very sweet
http://soundwood.weebly.com/uploads/1/5/6/5/15656028/aphex_fm_pro_model_2020_manual.pdf
Audio Prism
http://www.proaudiodesignforum.com/forum/php/viewtopic.php?t=763
Innovonics David....there are many similar products.. note the gentle filter slopes
http://www.inovonicsbroadcast.com/uploads/2017/03/31/718%20Manual%20%20(5.2.14).pdf
the orban ftp site has a number of manuals for their split band products.....they were rather to fond of epoxy modules

or how about the Behringer MDX8000http://www.3-mtr.info/manuals/BEHRINGER/MDX8000/Mdx8000Rev3.pdf
I designed and built a three band unit for FM processing in the mid 80's.... IIRC Ispent a lot of time on the side chain circuitry, to prevent the unit sounding bad on high dynamic range or band limited material....It was in an on-air chain for about 5-6 years...until it was replaced with something louder and nastier.........
The next station I worked at used a hybrid system of Aphex compellor (to set the sweet spot...mostly levelling) followed by the multiband section of the innovonics 250, followed by Aphex Dominator (with the side chain timing modified)
As Rob notes the input effort can outway the results!

Cheers
tc

 

[djdonovan]

Than you tomcat! This is very helpful and in hindsight, broadcast tools should have been obvious given the need to control dynamic range.

I will dig into this

 

[djdonovan]

tomcat was your design analog or digital? In looking at the broadcast stuff so far, a lot of it is digital which makes sense from a cost/feature/form factor standpoint. I was kind of hoping for a solution in the analog domain. The L2 would be another option, but I'm not sure of it's leveling features.

The Behringer looks promising and I'm sure has lots of personality for what I am looking to do. Given its age, seems like I might have a hard time finding one without keeping my feelers out there for a while. I'll have to look into the Compellor

 

[abbey road d enfer]

Is anyone aware of a hardware multi band compressor that has auto makeup gain or expansion?

You need to make yourself clear about what you expect in "auto makeup gain". Proper auto make up involves analysing the whole content of a program and apply a global gain correction; so you need a preview facility and some kind of memory that will retain the result of a calculation. That specifically implies digital technology and non real-time operation.
I have a feeling you are on a different concept, which is basically AGC (Automatic Gain Control). It's a compressor with a very long release time, so that after an initial period of assessing the program level, the unit will keep its gain variation moderate.

In my mind wiring up 3 Valley People TA-101 VCAs through 2 selectable crossovers/3 bands and back to a summing mixer might do the trick

IMO this does not answer specifically your request of "auto make up gain". I believe you're trying to recreate one of the many broadcast FM processors that flourished in the 80's. What about giving a description of the intended application?

, but again I'm making a lot of assumptions on the feasibility of the electronics circuitry.

It is perfectly feasible.

I've also considering the idea of using a crossover to split the signals into 3 compressors/expanders, then mixing back together.

Isn't it exactly what you just suggested?

I've also heard mention of parallel compression used to get the effect of expansion.

Then you've been misguided; parallel compression cannot result in expansion.

I'm not so concerned about the noise floor as this is part of the effect, but it would make sense to have some sort of gating logic when the effect is used with extreme settings.

Maybe you should; all designers who have dabbed with multiway compression have had to consider solving noise issues one time or another.

I'd be willing to taking a stab at this on a breadboard,

Breadboarding what? Just breadboarding a decent compressor or a decent x-over ends up in a terrible mess, now think of building those 4 or 5 units plus a summer...

 

[djdonovan]

You need to make yourself clear about what you expect in "auto makeup gain". Proper auto make up involves analysing the whole content of a program and apply a global gain correction; so you need a preview facility and some kind of memory that will retain the result of a calculation. That specifically implies digital technology and non real-time operation.
I have a feeling you are on a different concept, which is basically AGC (Automatic Gain Control). It's a compressor with a very long release time, so that after an initial period of assessing the program level, the unit will keep its gain variation moderate.

I would agree that auto leveling/Makeup gain is what I am going after here. I was hoping to do this in the analog domain due to its sonic qualities, but I understand why it's commonly done in digital.

IMO this does not answer specifically your request of "auto make up gain". I believe you're trying to recreate one of the many broadcast FM processors that flourished in the 80's. What about giving a description of the intended application?

I think use of the OTT plugin from Xfer Records is the best example of how I intend to use this effect. It's less utilitarian and more of an intended effect that changes the transients of synth sounds, percussion loops, and more. In my case I intend to use it for loops as it pulls up the reverb tails and gives them a different sonic quality. Obviously this is a purely subjective use/effect. As was said before, broadcast applications seem to be an area that make a lot of logical use of this processing.

Then you've been misguided; parallel compression cannot result in expansion.

I assumed so which was why I mentioned the hypothetical need for two Maselecs to get the auto leveling effect to happen. One in compression mode and one in expansion mode in parallel (However in looking at the manual, there might be a way to link the two. It seems it is based off a specific type of sidechaining, so might only get halfway there). FWIW, I think there are some misunderstandings in threads/comments I have come across around the internet that seem to be related to Bob Katz's book and the terminology being used.

Maybe you should; all designers who have dabbed with multiway compression have had to consider solving noise issues one time or another.

Makes sense. I'd be curious how OTT handles it, but I would assume there is a gate in there somewhere that kicks in. There are no controls for it. One reason for me pursuing the analog route is the dithering/breaking apart of the signal once the input signal drops and there isn't enough to level up before the gate kicks in.

Breadboarding what? Just breadboarding a decent compressor or a decent x-over ends up in a terrible mess, now think of building those 4 or 5 units plus a summer...

Makes sense. I have no basis to compare to so knowing that is helpful

 

[pvision]

Setting the multiband part of your request to one side, the effects you're looking for are all time-dependent compressor effects. The previously-mentioned Compellor & Dominator would be ideal

The Compellor is an excellent AGC / Leveller which has (I suspect) a combination of very long time constants for levelling and a faster component to catch fast changes. These are managed so well that the effects are nigh-on inaudible

The Dominator has a peak limiter but also has a Density control which pushes transients back & forth in the mix. I think there's a high-frequency limiter in there (something like a Fatso) with a very short attack time which neuters the hard edges of transients. Again it's very hard to hear the Dominator in action. Switching it in & out seems to change the balance more than the dynamics

I think, if anything, they will be too subtle for what you want. But they might be a good starting point. The Dominator has a frequency-dependent section as well but it's predictably subtle

Photos & descriptions on my website:
http://www.bn1studio.co.uk/shop/compressors/aphex-compellor/
http://www.bn1studio.co.uk/shop/compressors/aphex-dominator-stereo-compressor-model-720/

Nick Froome

 

[topcat]

tomcat was your design analog or digital? In looking at the broadcast stuff so far, a lot of it is digital which makes sense from a cost/feature/form factor standpoint. I was kind of hoping for a solution in the analog domain. The L2 would be another option, but I'm not sure of it's leveling features.

The Behringer looks promising and I'm sure has lots of personality for what I am looking to do. Given its age, seems like I might have a hard time finding one without keeping my feelers out there for a while. I'll have to look into the Compellor

I used dBx VCA's and a whole bunch of op-amps.
The Behringer, in my experience is not the useful device one would expect..... I'd look at the Aphex 2020 for basic inspiration and structure and read the BBC R&D 1965 (?)  paper on limiters that describes the stacked RC timing networks.
I think tyhat one of the secrets of the Aphex devices is the non lineararity of the control law...which effectively gives you a soft knee characteristic.
The other device to think about is the analogue version of the Arriane which is based on the That 4301 'Compressor on a chip'...with shallow filter slopes.
enjoy

 

[Script]

TC Electronic comps.. But they're digital, so could just as well do ITB.

Breadboarding a multiband sounds like hell. And I'd expect splitting and summing the program signal to be crucial and a real pita.

The Dominator has three VCAs to accomplish the task, then sums the result and  sends it through a clipper. The inside of that box is insanely dense with components.

Isn't there a freeware version of Xfer by OTT?

 

[djdonovan]

Thank you all. This is all very helpful.

TC Electronic comps.. But they're digital, so could just as well do ITB.

Yep, a lot of this leads to an ITB solution which just takes me back to OTT.

Breadboarding a multiband sounds like hell. And I'd expect splitting and summing the program signal to be crucial and a real pita.

Give the feedback, would be clearly beyond my level of skill

The Dominator has three VCAs to accomplish the task, then sums the result and  sends it through a clipper. The inside of that box is insanely dense with components.

I will take a look at that unit based on the multiple mentions.

Isn't there a freeware version of Xfer by OTT?

Yes it's free, and worth at least a small fee IMO. Can be noisy as hell which is part of it's charm, but some of the noise when it starts to fade out and break apart and becomes very digital sounding. Which brought me to my original hope that there might be a similar solution OOTB/Analog. For the Dub and Dub Techno music I am doing, that noise would be a creative component to the track. I could fake it ITB and maybe mask it. I have a feeling this will lead me to some time consuming research into characteristics of digital versus analog noise.  :'(