Different types of compression, SSL vs 1176 vs 1a2a vs DBX160 ect...

[todd_r]

Hi Dave, would be interested in hearing what you think about the Golden Age comp -54 or the RNC (I've got no schematics I'm afraid) just because they offer new, cheap hardware ways of accessing either character or transparent compression respectively.

[flugel45]

Haven't read the whole thread, so I apologize if it's already been mentioned.

Here's an article from SOS mag on Classic compressors:

http://www.soundonsound.com/sos/sep09/a ... essors.htm

[Dean Aka Nekro]

Building a high-precision high-range logging amp WAS impossible, but by the time you get to dbx, they're selling ICs that have something like 80dB of range, which is fantastic!

What's a logging amp?

If you can demonstrate with some examples, we can (and should!) evaluate this, but I suspect the reality is that when you're monitoring software, your head is in the sweetspot, while when you're monitoring the outboard, your head is outside the sweetspot, and you're adjusting timings accordingly. I support this claim with the observation that half a wavelength of low mid is going to be in the order of a foot or two, which is probably how far you have to move your head to look at a unit you're adjusting.

What if you use headphones or test a render?=)

A logging amp is a waveshaper which generates y=log(abs(x)). You use it to convert a signal (which is a voltage) to a dB measurement.

I'd love to know if you find the same thing in cans, but further, if you find it with renders, we can delay compensate the renders, and phase cancel them!

Dave.

I'm not at all an expert or remotely close but reading up at this place is quite handy meloco_go http://www.proaudiodesignforum.com and an example thread in said forum - http://www.proaudiodesignforum.com/foru ... ?f=6&t=111, I cross my fingers that you'll agree Dave, Was it a joint design/build by Paul Buff and his then Wife Allison regarding the Dyna-mite? IIRC before Valley People Allison was doing alright releasing/selling at least one compressor I know of, The AR Kepex

All the best to everyone, Interesting reading

[DaveGamble]

Dave,

I was wondering if you could comment on the venerable Alesis 3630. I know its basically garbage, but I've been using them in non-music A/V applications for a long time, and know it better than any other compressor.

It's a dbx160 with cheaper components and a higher noisefloor.

Dave.

[Dean Aka Nekro]

[quote="V0RT3X


This is what i love about being a member at KVR!

Thanks for all this Dave!

I personally enjoy the DBX160 & SSL emulations.

What do you think about the valley people Dyna-mite? Is it pretty good for aggressive compression? (btw that rhymes )[/quote]

I can't speak on Dave's behalf V0RT3X but I can say that I really like Valley People DYNA-MITE on drum shells and indeed go rather heavy handed with application also. I ended up buying a license for the Softube model of it as they have done a good job to my ears/tastes of the thing. I'm certain you will have a lot of fun using it as you like using the DBX160 for drum/percussion, Its I suppose a 160's very badly behaved/savage cousin that doesn't get invited to get together's as it would be the one to start the brawling Its also very versatile for a 1RU piece that can be had used on ebay for example around £250 - £275. I'm a fan of/use DBX266XLs and Alesis 3630s though, Not exactly impeccable taste however for a lot of stuff they just work. I'd say that with Dave's COMPassion which is incredible btw Dave and time its totally possible to dial in very similar results or if Dave were to add them as mods sweet . Also good to speak to you mate/catch up as it has been awhile. I hope you are doing well and life is treating you good man. Obviously for what my very humble opinion is worth. I also have/use a few old Joe Meek opto compressors, JDK Audio R22 Compressor, Drawmer 1968 Comp, FMR's Really Nice Compressor + Really Nice Levelling Amp. Along with some higher priced and many similar priced bits. I'm wanting a Slate Pro Dragon after Shy demonstrated its capabilities and I then checked one out in person. I also love my LiquidMix Dave which you did right? Its a shame they didn't take it further IMO, Oh and my guilty secret is a modified Behringer Tube Composer Pro, I love the two I have and was gutted when they stopped doing them. There are a good many plugins that are better than much of the rack comps I have, Again IMO

All the best to you two gent's and to all as always

Dean

[DaveGamble]

DaveGamble,

I am not one to go out of my and understanding the exact inner workings of a compressor . . ., yet (starting to cut my teeth into circuit design because a big future goal that probably won't happen lol). Anyway, I do find I select compressors based more on the way the compressor behaves to material and that brings up a question that I have yet to figure out. It deals with a Vari-Mu style compressor, the classic Gates Sta Level. Now, my question is not so much about the way it compresses, which if memory serves it is a pretty simple program dependent circuit which has an interesting attack characteristic (something like a cross between an 1176 and a VCA depending on what you throw at it) but otherwise behaves more like an Opto. The question I have is why approach compression that way (I get that it was more meant as a limiter and it was like '56)? What advantage does that offer in terms of circuit design or even compression characteristics over say a transistor based circuit?

I don't understand the question, sorry. When you say "why approach compression that way"... what way?
Who is doing the approaching? The designer of the Gates?
Are you asking me why the designer of that unit designed it in a particular way?
Most likely it was a circuit that he COULD make. Frankly, achieving 40dB of compression range with a valve design is extremely good going! He'd have every right to be proud of that.

What advantage does it offer in terms of circuit design over transistors.. what, using valves...? In 1956?
You do know that the first WORKING transistor was made in 1954, right? I mean, you literally didn't have a choice of using anything but valves. You did what you could with the components you had. This is the whole story of audio design.

There's a massive segment of pro-audio history I like to refer to as the "op-amp race", where designers were competing to build the most accurate op-amps they could.

Now you pull a 5532 off the shelf, and pay 0.1c for it.

Dave.

[DaveGamble]

this thread makes my coffee taste that much better.

I swear Dave, if Compassion shown up in my life years earlier it would have convinced me to switched over to EE major

[DaveGamble]

Hi Dave these are probably better examples:

SoundonSound media from their Portico plugin review tested against the hardware. The plugin seems excellent and as documented in the review they spent a good deal of time tweaking them...only when I directly switch between the loops whilst playing do I hear the slightly differing quality. To my ears its hard to tell sometimes the high end is more open, but on the 3 examples Ive included - all of them I was able to distinguish slightly more low mid punch and generally a sound that was a fraction firmer/together in the HW example...when listening Ive just been using my HD650 Headphones today but they are decent for finding detail possibly more so than a so-so monitoring set-up...

https://dl.dropboxusercontent.com/u/799 ... amples.zip

Though I don't have schematics for the Portico, I will observe that it features both Feed-forward and Feed-back modes.
If you ask Andy Simper (who is rather the king of such things), modelling feedback circuits without cheating is extremely fiddly. I have no reason to believe that Yamaha have any experience in that field at all. Frankly, the idea that they could compete with Andy in the art just seems absurd to me.

I think we should do this with something really straightforward like a dbx, which has every reason to be perfectly modelled.

I was thinking I might make a blind testing plugin, where you can route in two signals as input and sidechain, and it tells you how you did. Any interest? Is there such a thing floating around already?

Dave.

[DaveGamble]

Which leads me on to one question that im not sure has been asked in this thread ; saturation, harmonics, distortion, etc from compression. Basically, what is the 'story' here. Does it exist in compressors, does COMPassion do it or how would i incorporate it. I know its a long one so if you have a link im more than happy to read.

+1 on hardware presets for COMpassion !

Ok, first off, saturation = harmonics = distortion. All three words meaning the same thing.
In the hands of a designer, these words insinuate different types of distortion, but in any case, all distortion.
What these words all mean is that if you run a sinewave in, you will get harmonic copies of the sinewave out.
Saturation /tends/ to imply that if you put a sinewave in quiet enough, you'll get just the sinewave out, and increasing the level is needed to get harmonics out.

Does compression (ANY compression) generate harmonics?
YES. Definitely. But unless attack and release are VERY fast, they're likely to be pretty low-level.

Compression inevitably involves multiplying the input signal by a gain reduction signal, and MULTIPLYING signals together (think ring mod) ALWAYS generates some new frequency content. HOWEVER, if the GR signal is slow moving (has no edges, and no high frequency content), then that distortion will be extremely low level. On the other hand, if you kill the attack and release, so it's grinding the signal, you'll hear plenty of distortion.

Multiplying signals in analogue and digital work pretty much the same, except that you can do it with absolute fidelity in the digital domain, and in the analogue domain, it can sometimes crap out on you (see GR range, etc).
With a poorly designed VCA, you can end up with distortion even when the GR is doing nothing. Which is a reason for liking optos ('cause you can design 'em cheaper, and avoid distortion). The FET in the 1176 is nice too, 'cause when it's doing nothing, it's really doing nothing Making a good VCA is EXPENSIVE (well, not nowadays, of course, but it WAS!)

The one exception between analogue and digital domains is aliasing, which just doesn't happen in analogue. Different domains, different problems. This is why for aggressive compression, oversampling is a boon. Also, for simulating difficult circuitry, oversampling simplifies some parts of the process, but that's by-the-by.

Are there units that can impart character because of their input or output stages?
Probably, yes. But when you design a unit, you're always trying to keep the THD+N (what comes out that didn't come in. Total Harmonic Distortion plus Noise) as low as you can. So pretty much everything ever is designed to be inaudible within the operable range of the compressor. I can't rule out that there's a box where you consistently crank the makeup gain to distort the output... but when it comes down to it, that has NOTHING to do with compression - it's reamping!

Dave.

[APZX]

Gamble,
Sorry I was not quite clear enough with my question

I understand that the first working was transistor was 23 December 1947 at Bell Labs (thank you Google). And frankly the transistors were probably not all that efficient at doing a whole lot back then anyway. So, allow me to rephrase the question.

Would the approach taken with the Gates Sta Level still be a valid approach today? Or more accurately what I'd like to know, is what might be some of the reasons to approach compression the way the device did?

Now, I get that you're not the designer of the original and I'm not expecting that. But more I'd like to understand a bit more of the possible conceptual idea behind the circuit. Even if it is just a best guess. An example that does not deal necessarily with a strict compressor, but De-essers (HF limiters more or less). There are a multitude of ways to approach that particular problem. Ranging from a simple HPF feeding into a sidechain to more complex phase cancellation designs. But they all strive to do the same thing, remove excess sibilance. I'm just looking for a best guess on why one might approach compression the way that the Gates Sta Level did.

[DaveGamble]

I agree the dbx models are close and pretty good...in fact in an ABX test machine its really quite tough to distinguish...but once you get your ear in - the kick is one thing, but also the way the compressor clamps around the clap...in both examples its just slightly more enveloping the sound and holding a bit more bass...really if you are good at mixing its not going to cause a huge change, but still its a characteristic I tend to hear...

Im starting to wonder if the fact that software carries all freq esp subs but hardware filters out some sub and higher freq making it sound punchy...(as well as a bit of saturation?)...

Probably, yes.
I'll admit it, when modelling circuits, the 1Hz HPFs tend to get ignored.
This is because, while people say that they add up... if you actually add them up, they don't. They're negligible.

But if there's some hardware that really is rolling off the top end, and has a cutoff at 20khz (so you're 3db down at 20k), that SHOULD be part of the model. That makes a massive difference actually. Give that a try - insert a 20khz HPF (a good one, mind! one that doesn't just bypass, and not one that BLT cramps!!!) before your model and see if it helps any.

But we should do this with science, because we can! Anyone know of an ABX testing plugin around, or am I knocking one together tomorrow?

Dave.

[softska]

Anyone know of an ABX testing plugin around, or am I knocking one together tomorrow?

Windows always have the mighty foobar2000 w the ABX Comparator component. On OSX ABXTester is barely usable I guess, can't remember if there's anything else available

But if there's some hardware that really is rolling off the top end, and has a cutoff at 20khz (so you're 3db down at 20k), that SHOULD be part of the model. That makes a massive difference actually. Give that a try - insert a 20khz HPF (a good one, mind! one that doesn't just bypass, and not one that BLT cramps!!!) before your model and see if it helps any.

the sidechain, output, or both?

[DaveGamble]

Hi Dave, would be interested in hearing what you think about the Golden Age comp -54 or the RNC (I've got no schematics I'm afraid) just because they offer new, cheap hardware ways of accessing either character or transparent compression respectively.

The comp54 is a 2254 clone, right?

The 2254 is a mass of incredibly carefully calibrated discrete (read: transformer) circuits. And it appears to be using a diode bridge for the gain control. Which is quite something. Looks pretty similar to the 33609... but embellished to keep it quieter.
It's /almost/ fair to say that it's made out of carefully crafted op-amps (it's definitely part of the OpAmp race part of history). Alas, the schematics I have, I find I can't read as quickly as straight opamp circuits, so I'm still ploughing through, but it looks pretty no-nonsense; just carefully tuned to be as invisible as possible (in terms of THD+N) at every stage. As for the compression characteristics, I can't just read them off the page by looking; discrete circuits are a little more opaque than valve/opamps.

If I get anywhere I'll post results.

Dave.

[SWAN808]

Great Dave!

I use this:

https://itunes.apple.com/gb/app/abxtest ... 4135?mt=12

Re Portico it has the Feed Forward also but yes we could look at the dbx also...just wondering did you listen to the portico and hear any of what I was talking about?

[DaveGamble]

Haven't read the whole thread, so I apologize if it's already been mentioned.

Here's an article from SOS mag on Classic compressors:

http://www.soundonsound.com/sos/sep09/a ... essors.htm

Nice link!

Dave.