Opto vs. VCA

[Debutante]

What is the definitive difference between the two? It sounds like opto is a little more deliberate (noticable), or colouring, or non-linear or something like that, but how best would you describe it to newbie me. CHEERS!!!!!!

[The Chase]

opto? where did you see it?

[beej]

You're talking about compression characteristics?

Opto usually has a slower overall characteristic, is often softer or smoother. Often the compression starts at below the set threshold but at a really shallow ratio, and ramping up to the desired setting.

VCA type tends to be firmer and tighter. I generally go for opto on vox and VCA for anything percussive, but it really depends on the material and what you prefer at the given time.

Also, it really depends on the particular compressor's implementation.

[Debutante]

I was thinking of trying opto on percussive elements that don't mind extensive modiffication, like a loop for example, and yes I was talking about compression. I deliberately avoided saying so in the header hoping to attracting a more succinct reply, which was more likely to come from someone who knew what the terms meant. Cheers! I could hear a difference but didn't know quite what is was and why it sounded like that.

[beej]

Here's an excerpt from the Waves RenComp manual on it's Electro/Opto compression modes:

"Electro (the original mode of the v1.0 software) has a release time behavior that is increasingly faster as the gain reduction approached zero, but only when gain reduction is less than 3dB. When GR is above 3dB, the release time becomes slower, behaving more like a leveler in high gain reduction situations. Therefore, when used with moderate compression, the Electro mode produces a great increase in RMS (average level), and is ideal for "loud" applications, such as voiceover and certain genre of music.

Opto is actually the inverse of Electro. Opto-coupled behavior always "put on the brakes" as the gain reduction approaced 0dB, i.e., the release time gets slower as the "needle comes back to zero". As in Electro, this is true only when the GR is less than 3dB; when greater than 3dB, the release time is faster. This is the vintage emulation that sounds so great for drums and more! "

"Remember that Opto-mode provides fast release times when the gain reduction is above 3dB, and progressively slower release times as gain reduction falls below 3dB. This is very much like opto-coupled hardware compressors.

Electro-mode has the opposite characteristic. Electro-mode provides very fast release times when the gain reduction is less than 3dB and an overall slower behavior when gain reduction is above 3dB. "

Again, it really depends on the compressors implementation, so just give the settings a try, read the manuals, and go with what works best for you...

[Debutante]

Thanks for the article! This is what I meant when I said I was thinking of using opto on certain percussive elements. I was not, however tuned into the 3db "rules" as mentioned above. It sounds like something unique to that particular compressor, though. CHEERS!

[bobby yarrow]

Also, it really depends on the particular compressor's implementation.

That's the whole story. While the generalities are right, every compressor is different. If you're picking between emulations, knowing the generalities will be helpful. If you're picking between hardware units, not so helpful.

[michu]

differences in actual modelled hardware aside, the so called 'opto' in digital realm usually involves feedback detector (ie detector is fed from the gain reducing stage it controls) while 'vca' is usually feedforward.
Endorphin's manual on the digitalfishphones site has great explaintation of that stuff

[bobby yarrow]

I know shockingly little about how software is implemented. Never occurred to me that they might code for things like shunt or series implimentation of the gain control, or feedback or feed-forward. I assumed they just changed the knee, attack characterstics, and distortion/harmonics a bit.

[bobby yarrow]

As an aside: First off, opto/elop compressors tend to be less noticable than vca's, or at least old-school DBX vcas. Second off, there's a bunch of other ways to make a compressor. A compressor is basically an attenuator that uses a sidechain to control the attenuation. FET and variable mu circuits are also common, and have different typical characteristics. But, as we've been saying, the differences in modern hardware have a lot more to do with implementation than class of compressor.

[beej]

I know shockingly little about how software is implemented. Never occurred to me that they might code for things like shunt or series implimentation of the gain control, or feedback or feed-forward. I assumed they just changed the knee, attack characterstics, and distortion/harmonics a bit.

They range from simple to complicated. For example, the UAD plugins are component modelled - they have models of how *every hardware component* behaves and interacts in the emulations, even down to things like how many photons are emitted and detected in the opto circuits for the LA2A for example. It's why they feel so complex and satisfying...

[bobby yarrow]

I'm really going to have to learn more about this stuff. I know that UAD claims to model at the component level, but how that translates into code is mysterious to me. I hate relying so heavily on tools that I don't understand at all.


Of course, I don't really understand how sound goes down a wire . . .

[beej]

Try hanging around in the DSP forum here. You'll soon prefer not understanding once you start getting into DSP...

[stefancrs]

In the last VST release of our synthmaker compressor I added an opto mode
http://www.kvraudio.com/forum/viewtopic ... 76#1859876

If anyone got any interesting yet simple "opto" way of doing expansion, let me know! I'm not after modelling any hardware or anything, I just enjoy having two different flavours available in the effect.