Compressor Round Up...

[taliska]

Hi all,

So, late last night I was searching around on google reading up on various compressors, as I've been figuring out which ones are usable on mix bus and which are not.

Anyway, I accidentally stumbled upon http://www.soundonsound.com/sos/sep09/articles/classiccompressors.htm, an old sound on sound article from '09, and noticed that there was a compiled list of favourite compressors and their applications by various prominent engineers.

Anyway, it occurred to me that there are various compressors that are on that list that are never mentioned in these forums and I figured it would be nice to do a little compressor round up, based on architecture, applications, whether DIY versions are available or for those that are off-limits DIY-wise, whether similar-ish DIY-able builds are available from a topology perspective.

I suppose this is meta territory, but I don't remember seeing such a thing in the meta, so if this seems like duplication or off topic, please feel free to move/delete as appropriate. I've taken a look in the meta recently, and it seems a bit more project specific, so I don't think this is duplication, as this is more overview-y than that.

I'll copy and paste the list here as a starting point. Someone should say hey, if they think I should obscure any of the names, but for now I'll leave it as is. Post to get anything you want added. Once it's added, remove the body of your post to keep things tidy.

Some were already grouped together in the original article, so I've kept it the same, but if there are ones that shouldn't be grouped together, then just mention it and I'll split them out. Obviously, some compressors are good for lots of things, so they can appear in each of the applicable sections. I'll probably cull clones that don't do anything new, or ones that try to clone all the various types (you all know which one I'm talking about here...), and ones that are actually complete channel strips.

And if anyone thinks there's a better format, then just post demonstrating the format, and if it looks better I'll adopt it.

Also, it would be nice to just hear about opinions and experiences with any of these, specifically, if you've found them useful for particular styles of music, as that would be another nice thing to add and any additional context like why one particular VCA based compressor is so much better than another VCA based compressor for drums, but not for vocals, or whatever.  Obviously that's more something for Studio A, but I don't really want to split this post up, so...

Kaz

P.S. There's already a section for drums which I guess covers bus compressors in general, but if anyone thinks general bus compressors are different enough to warrant an additional section, I'll add it...

CLASSIC VOCAL LEVEL CONTROL

Model	Type	Similar To
Dbx 160-series	VCA	?
Focusrite Red 3	VCA	?
Summit TLA100 & DCL200	Tube	?
Teletronix LA2A & LA3A	Opto	?
Tube Tech CL1B	Tube	?
Universal Audio LA2A	Opto	?

VOCAL COLORATION & ENHANCEMENT

Model	Type	Similar To
Fairchild 660 & 670	Tube	?
Universal Audio 1176	Fet	?
Urei 1176 & 1178	Fet	?
Altec 436	Tube/VariMu	?
Collins 26U1 & 356E1	Tube/VariMu	?
Federal AM864U	Tube	?
Gates Sta-Level	Tube	?
RCA BA6A	Tube	?
Universal Audio 175 & 176	Tube	PRR-176

DRUMS

Model	Type	Similar To
API 2500	VCA	?
Dbx 160X	VCA	?
Fairchild 660 & 670	tube	?
Neve/EMI TG12413	?	?
SSL G-series console master compressor	VCA	GSSL, MixBuzz, SB4000
Urei 1176 & 1178	Fet	?

BASS

Model	Type	Similar To
Joemeek SC2	Opto	?
Urei 1176	Fet	?
Teletronix LA2A	Opto	?
Gates Sta-Level	Tube	?

 

[hymentoptera]

I remember reading this article and thinking it's a strange list really. Some of those compressors don't belong on that list, while others are painfully missing.

Like the dbx 160X, I mean, you can buy those used for dirt cheap. Awesome compressor, everyone should have one, I think I gave US$145 for mine about a year ago, and right now it's loaned out to another studio where it apparently "saved a vocal session" that was otherwise not going well. But I could think of ten other compressors that would easily belong on that list before the dbx 160X.

 

[emrr]

I'd never use a 26U or BA-6 type on a vocal, but plenty of people do.  They pump and wheeze in an obvious manner too much of the time.  They work much better on drums, acoustic guitars, piano, etc. 

 

[hymentoptera]

Some of these, like the API 2500, are still in production.

But I think a Federal AM864U clone would be wicked! I don't think that one's been done as a DIY yet. I've wanted on ever since I read about it in Tape-Op a while back. It's an old military radio tube limiter that's supposed to pretty insane!

 

[taliska]

Some of these, like the API 2500, are still in production.

I wasn't sure whether it would be clear from my initial post, but this isn't meant to be specifically a DIY shopping list as yes, some compressors are off limits as they are still in production. For those, my hope is that we can have a conversation about the differences between the various designs in production or not, and talk about what makes certain things unique.

I don't know much about compressor design right now, but it would be nice to get to a point where some of the finer points of side chain design had been discussed, as it feels like to me, that's where the majority of care and attention should be placed when considering designing a compressor or weighing up which of the various designs to build.

I'm kind of a "paint by numbers" guy at the moment, but one day, if I was able to find the time, it would be nice to create a mash-up compressor for the community. Not for anything but fun and experimentation as I already have a day job.

As a first step in the discussion, it would be nice to talk about whether it would be possible to build a modular platform for experimenting with side chain designs, as that to me, seems like it could be a little bit "plug and play" and could serve as a jumping off point for anyone wanting to try their hand at it...

 

[ruairioflaherty]

Sidechains vary enormously depending on topology, an LA-2A needs 100V to drive the panel and a VCA compressor needs millivolts in DC…

As for the API 2500, if the ethics of cloning it don't discourage you the the sound of it certainly should.  Hugely over rated IMO.

 

[taliska]

Sidechains vary enormously depending on topology, an LA-2A needs 100V to drive the panel and a VCA compressor needs millivolts in DC…

Indeed, and that would probably make one more suitable for experimentation than the other, right?

As for the API 2500, if the ethics of cloning it don't discourage you the the sound of it certainly should.  Hugely over rated IMO.

I thought I was clear on this.

The goal is not to clone the API 2500 or any of it's off limits friends.

However, talking about what makes it special or not, shouldn't be off limits, if we're just talking. Perhaps there's something there to take inspiration from, (or not, I've never used one),  either way, it can only be educational to look at it. They (API) say their thrust circuit is patented and that's fine. Off limits. So the question becomes, what is is it doing and is it anything special in reality, or just some kind of time dependent frequency sculpting in the side chain?

Oh, and I'm a software engineer by trade (games & 3d stuff), and I make products to sell on behalf of my own company, a one man band as it were. I'm more than versed with the ethics of copying IP or not and the effect that might have on an existing business. Software is pretty much at the sharp end of IP these days, patent trolls are everywhere, and it seems every potential customer thinks my product should be free, and every competitor thinks it's ok to decompile my software to extract data to use directly in cloning my games, and yet I pay for the software I use and try to build original products. So yeah, I might be a bit foolish perhaps, but generally not lacking in ethics, unless the DIY audio gear I've built so far has actually been an exercise in breaking the law?

One more time in case this thing isn't on:

This isn't a "let's rip off compressor A" thread, it's a "the reason it's suitable for this kind of application is because is because of this particular feature which is X at a technical level" thread. Think of it as the original SoS list with technical observations on similarities between compressors chose for the same job.

So to take another tack:

The SSL is a great bus compressor, or at least the mixbuzz 500 I have is. Very hard to make it "pump" intentionally, something I've been trying to do as an experiment in making French House and which I'm currently doing ITB using the logic compressor with a side chain track. Word on GS is that the French house sound is the result of having a crap compressor across the mix...specifically the Alesis 3630/3632. Pointless to clone though as it's a very cheap unit and I can pick one up for less than a new case if I wanted to build one myself.

Both of those are VCA comps...actually, so is the 2500, so let's discuss how they are different and how that might affect their compression characteristics...

 

[hymentoptera]

Ok. Well, another point of discussion might be feedback vs. feedforward designs.

If interested in developing a modular compressor it could be useful to search for information on modding existing compressors where details can be found on how their sidechains actually work. VCA feedback types will probably have the most in common, and so be the most likely candidates for a modular compressor. But I could be totally wrong.

 

[taliska]

Ok. Well, another point of discussion might be feedback vs. feedforward designs.

If interested in developing a modular compressor it could be useful to search for information on modding existing compressors where details can be found on how their sidechains actually work. VCA feedback types will probably have the most in common, and so be the most likely candidates for a modular compressor. But I could be totally wrong.

So I'm not well versed on the benefits/draw backs of each, but my initial thought after looking at a simple flow chart was that a feed forward would be the better choice because it's behaviour is much more predictable. The feedback method looks like there's more error in the reduction due to the cyclic nature, though obviously, after reading about it, it's clear that that is a strength also as it seems to lead to a more gentle reduction in gain.

I found a great document by the Elysia guys about feed forward vs feedback actually:

http://www.elysia.com/company/stories/forward-or-backward-2010/

TL;DR: Feedback made a lot of sense when VCAs weren't available as it made the component tolerances something that could be lived with. The precision of VCAs make feed forward a more sensible design going forward.

Clearly I don't know very much yet, but just thinking out loud. If I were to try and build something, I think I would want to try something VCA & feed forward based, and avoid re-treading old ground. The goal to create something with powerful shaping possibilities that is fundamentally clean. Of course, being a software dev, I do have to ask myself whether it's not something I could play with more easily by writing a plug-in, but then where would be the fun in that...I came here to get away from my day job!

;-)

(I've actually already written a limiter for my game audio engine, so that environmental sound effects, of which there may be many or none, don't overload the device output...but I created it years ago, so it doesn't try to do very much. Instant attack and release, accumulates samples in to an RMS buffer that is used to adjust threshold and auto gain...)

 

[pstcho]

Hello there, i have a pcb with limited info and don't know in what direction fit the vtl 5c9

Could you take a look please ?

 

[scott2000]

know in what direction fit the vtl 5c9

That is a little confusing to me as well . May be a case where it's safe to assume it goes by the shape when looking from top but who knows. No schematic?
Could see if it has any similarities another compressor.... Weak Joe for example, Pin 2 to ground, and one of the ldr pins to ground, the other to an op amp non-inverting pin..... Can't imagine it wouldn't go with the shape though....

 

[fallout]

The notch \ should be the negative leg of the LED. Older vactrols (Vactec) had a notch in the bodies to make this more obvious.

 

[pstcho]

Oh great, thanks for the help

Unfortunately i have no schematic and to my understanding it could work both ways

On the vtl there is no notch unfortunately

I'll try as you said and hope it won't burn

 

[gyraf]

..on the LED side, the long pin is plus, the shorter pin is minus. The two thin wires are the LDR..